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Associate Professor
Posts: 1,250
Member Since: ‎01-27-2009
Message 1 of 499 (70,560 Views)
Accepted Solution

Guide for Selecting a Power Supply

Mod may want to make this a STICKY.


Here's a general guide on how to select a PSU for your HP desktop.  The majority of standard ATX powersupply (PSU) should fit inside an HP case.  The exception would be a slim line case or the esoteric Blackbird. 


Look for an 80+ certification on the PSU to save electricity.  A PC will normally idle or run at low load 75% of the time.  Therefore, look for a PSU that's more efficient in the 50-90W range.  An 80+ 350W PSU reaches the 80% efficiency level at 70W output (20% of rated output).  The output must be greater than 140W to achieve the same level of efficiency from an equivalent 80+ 700W PSU.  So picking a PSU that is rated 25% higher than the maximum ACTUAL load of the rig will save you more $ on electricity. 


A modern PSU is designed to achieve peak efficiency between 20 and 80% of the rated output.  Running a PSU above the 80% load level will result in excessive heat, noise, and premature failure.


An Nvidia rig with GeForce GTX 280 (1024MB on board RAM) will draw about 350W max from the wall.  If we factor in the efficiency of a 80+ PSU, then the actual load on the PSU is only 280W (350 x 0.80).  To calculate the required PSU, multiply the actual load by 1.25 (25% margin).  In this case we only need a 350W PSU (280 x 1.25) to run this GPU.


Let's apply what we know to a Radeon HD 4870 (512MB on board RAM) rig.  290W max from the wall.  Actual load is 290W x 0.80 or 230W.  Now apply the 25% margin rule and we arrive at a PSU requirement of 290W (230W x 1.25).  Even if we apply a 50% safety margin, the power requirement is still under 350W (230W x 1.50).


There is no need to overspec the PSU by 50% unless you run your PC at full load 24/7.  Keep in mind that there is a huge variation in PSU quality and rating.  A cheap 500W PSU may not be able to deliver as much power as a quality 350W.  Antec Earthwatts/NeoPower/TruePower, Corsair, and Seasonic are quality units widely available at many US retailers.


Many high-end PSUs will need additional power from the PSU in the form of one or two 6/8 pin GPU power plug.  You can purchase an adaptor to convert a 4-pin molex to 6-pin GPU power plug.,2122-3.html

Accepted Solution

Re: Guide for Selecting a Power Supply

Hi Nautsj,


You should open up your PC and measure the physical dimensions of your power supply. Here is a list of things to consider:

1. Specifications
2. Total wattage - important
3. 12+ volt amperage rating - important
4. Modular - not mandatory but I like the flexibility
5. Warranty
6. i7 and SLI ready
7. Efficiency rating
8. Cost
9. Physical size -- standard ATX PSU is 5.5" by 5.9" by 3.4" give or take a few tenths
10. A single 12+ volt rail is a better choice. has lots of PSUs choices. Corsair, OCZ, Rosewill, Thermaltake.....


The typical EVGA GTX 570 in 9" in length.  The slot adjacent to the PCI-E x16 slot need to be vacant.  Open up your PC and do some measuring so that you know for sure if the card will fit.  I believe it will fit.


As for a power supply, the Corsair CX600 has very little growth but the Corsair HX650 will give you plenty of room to grow.

I am using the HX650 in two PCs.  It's a modular model so you have better options with the cable selection.


The HP "how-to" articles should be helpful.

TIP: When installling the power supply, unlatch the optical drive and slide it forward to ease the removal and installation of the new power supply.

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Associate Professor
Posts: 1,250
Member Since: ‎01-27-2009
Message 2 of 499 (70,368 Views)

Re: Guide for Selecting a Power Supply

[ Edited ]

Found a review of the Corsair 400W (Seasonic-built power supply) that I've been recommending on this forum.  This ATX power supply should fit inside most HP case (minus Slimline).  It has ample power to drive a modern quad core plus Radeon 4870 or GTX280 video card. 


At 100% load, we see a 2.5% drop in the +12VDC rail, which is still within spec and does not affect the performance of any component inside the PC.  +12VDC regulation at 82% load is a superb 0.5% with 45C case temperature.  Note that the power output and efficiency decrease with higher temperature. 


Cheap power supplies are rated at 25C.  When these units are subjected to higher case temperature, the output can drop 10-20%.


Again, we discover the sweet spot of a good PSU is 20-80%.  A good 400W PSU is more than adequate for many PC users.  This Corsair is only $30 after a $10 rebate.  That's a great price for a quality/quiet PSU that won't put a huge dent in your wallet.

Additional 20% off w/ promo code "Mar20", ends 3/31

Message Edited by RoyalSerpent on 03-08-2009 11:40 AM
Message Edited by RoyalSerpent on 03-08-2009 11:42 AM
Message Edited by RoyalSerpent on 03-08-2009 11:45 AM
Associate Professor
Posts: 1,250
Member Since: ‎01-27-2009
Message 3 of 499 (69,988 Views)

Re: Guide for Selecting a Power Supply

Here's a quick review of the Antec Earthwatts 380W power supply (Seasonic-built 324W continuous @ +12VDC with 50C ambient) coupled with Abit IP35-E motherboard, E8400 CPU (CO rev), Radeon HD 4870 video, 2GB Kingston PC2-6400 "N5" RAM, Panasonic 3.5" floppy, and 320GB Seagate 7200.10 hard drive.


The voltage and actual power numbers were obtained with calibrated equipments traceable to the NIST.  The E8400 has a thermal design power of 65W, thermal specification of 72C, and VID voltage range of 0.85V-1.36V.  The default CPU voltage went from 1.25V to 1.38V in the BIOS to permit overclocking.  This will probably raise the thermal power of the CPU to the 130W range.  Also added 0.2V to the RAM voltage (2.0Vdimm) to permit speed up to 493MHz at 5-4-4-9-37-2T timing.  Other BIOS voltage settings are at the minimum default.


This E8400 tops out at 4.2GHz (quad-pumped to 1868MHz FSB) under Orthos.  Although the core CPU voltage is set to 1.38 in BIOS, actual full-load voltage is around 1.35 due to Vdroop + Vdrop.  The Big Typhoon modded with 120mm x 38mm medium speed Panaflo maintains a CPU load temperature of 62C with 75F ambient air.  Although this chip is rated for 72C operation, its stability under Orthos decreases dramatically above 65C, possibly due to the high FSB speed.


This rig is capable of calculating the number Pi out to 1M digits in less than 11 seconds.





1). System OFF...3 watts (one red motherboard LED lit)

2). CPU and GPU at idle...96 watts (C1E and EIST enabled to reduce CPU core speed and voltage when idling) with +12VDC rail at 12.09V

3). CPU and GPU at 100% load...224 watts with +12VDC rail @ 12.02V


The noise from the PSU is barely audible at 224 watts load (three foot distance in a quiet room).  Efficiency is just under 82% @ 224W load.  Ripple-noise is a very respectable 21mV.  Although labeled as dual rail, the Earthwatts 380 is a single +12VDC/27A 50C continuous power need to balance-load each rail to achieve rated output.


Even with an optical drive and 8GB RAM, the peak load of this rig should remain well below 80% of rated output.

Posts: 13
Member Since: ‎03-01-2009
Message 4 of 499 (69,816 Views)

Re: Guide for Selecting a Power Supply

I just bought a new HP d5200t desktop. The factory website says it will come with a 460 Watt PSU. However, these computers only come with a 385 watt PSU.


I previously had a HP d5000z only a year ago. Same thing. The factory build it yourself page says it will come with a 460 watt PSU. It is actually shipped with a 385 watt PSU.


A call to HP tech service to ask about this difference brought me one of the biggest stories I have ever heard! They told me on three different ocassions that HP has a "way" of managing the electrical needs of the computer so that a 385 watt PSU is adaquate. I repeated my question. The website says you will get a 460 watt PSU. Why don't you get what you are told you will get? They just kept repeating the same story line. I might expect this from another company but I must admit this behavior surprises me when it comes from HP.






Posts: 13
Member Since: ‎03-01-2009
Message 5 of 499 (69,750 Views)

Re: Guide for Selecting a Power Supply

I should have said that my new desktop d5200t has two hard drives and the new nvidian 1 GB video card. Nvidia emailed me saying the power draw for this video card runs from 400 to 600 watts depending upon what you are doing. Using the 80% factor on a Power supply the power requirement for ONLY the video card EXCEEDS the power of the Power Supply.


My HP d5200t also has the Titainium sound card. The factory emailed me and said the power requirement for this sound card is 150 watts.


My CPU is the 3 Ghz core 2 duo processor made by Intel. An email from Intel tells me the power requirement for this CPU is 135 watts.


Using a mean average of 500 watts for the Nvidia card plus 150 watts for the sound card plus


the CPU requires135 watts equals 785 watts


thank you,





Associate Professor
Posts: 1,250
Member Since: ‎01-27-2009
Message 6 of 499 (69,735 Views)

Re: Guide for Selecting a Power Supply

Return the unit on the ground of false advertising.  This is the new HP.  Make $ anyway you can.  GM went down the same path, and is now heading to bankrupcy court.


I've testest quite a few GPUs.  A high-end Nvidia GPU will draw a peak load of about 120W.  The folks @ Nvidia is probably telling you to use a 400W PSU.  If the GPU is pulling 400W, then its heat sink must be 3x larger than the CPU's heatsink (nominally rated for 120W load).  It is possible that a GTX 295 may approach the 160W mark.


What is the model number of your Intel CPU?  That 135W number is for a high-end quad core chip like the QX9770.  The top of the line dual core E8600 (3.3GHz) has a thermal design power of 65W.




Wost case scenario...



-GPU...150W (GTX 295?)

-HDD x 2...40W

-optical drive...15W



Total maximum load 370W.  Add 25% margin to arrive at a rated PSU load of 462W!  Hmmm...  This is will the GPU, CPU, and HDDs working at 100% load (almost never under normal use). 





More realistic scenario...

-CPU...135W (quad core)


-HDD x 2...40W

-optical drive...10W



Maximum load 305W with 381W PSU.


So what would I do if I was in your shoes?  Demand a 460W PSU or your $ back.  Note that my calculation is based on a high quality PSU that can deliver at least 350W continuous at the +12VDC rail with 40C ambient air temperature.  A cheap PSU rated at 25C may lose up to 10% of rated power at 40C ambient.  That Corsair CX400 should work well.


The cheaper HP PSUs are not very reliable.  You can pop the case and write down the specs and model number of that PSU.

Posts: 2,158
Member Since: ‎11-17-2008
Message 7 of 499 (69,779 Views)

Re: Guide for Selecting a Power Supply

[ Edited ]

Hi SilverWhiskers,


I'm sorry to hear about your frustration in dealing with support. I just looked up your product specifications:


It does state that the power output wattage is 460W.


How did you find out there is only a 385 Watt PSU? Did you open the PC and read the label on the PSU?


I wanted to make sure the information on the Web was accurate so I found a d5000t and looked at the PSU inside the PC. And I think I may have found the problem.


I think there may be some confusion when reading the PSU label. The Max power of the PSU is 460W. However, there is a specification on the label that could be easily misunderstood. There is a part of the label that says THE TOTAL POWER ON.... NOT EXCEED 385W.


If this is what you saw, then you really do have a 460W PSU. That "not exceed" rating is based on total continuous power usage and this is common across the industry. The "extra" wattage between 385 and 460 is for handling power spikes.


Let us know if this is what you needed or if there is something else telling you that your PSU is not the right one for your PC. HP employee just trying to help where I can, but not speaking on behalf of HP.
Associate Professor
Posts: 1,250
Member Since: ‎01-27-2009
Message 8 of 499 (69,741 Views)

Re: Guide for Selecting a Power Supply

[ Edited ]

Then it's false advertising if you label a 460W PSU that can only deliver 385W continuous.  It is clear that the intention is to mislead un-informed consumer.  Peak power output rating is meaningless, since the PSU could potentially deliver up to 700W for 1mS. 


Way back when, the home audio manufacturers were making outrageous output spec based on peak power @ 1KHz.  The FTC stepped in with the RMS requirement.


The el cheapo garbage PSU will come with glorious label like 500W, then in tiny text on the PSU, we see something like not exceed 400W @ 25C!  It appears that this HP PSU is a 380 watter.  We still don't know if this output is @ 25C or 50C. 


The $30 entry-level Corsair CX400 is rated to deliver 400W continuous at 40C ambient, with a maximum of 360W to the +12VDC rail. 


Antec Earthwatts 380 is rated to deliver 380W continuous at 50C, with a maximum of 324W  to the +12VDC rail.


Enermax 500 is rated to deliver 500W continuous at 40C, with a maximum of 432W to the +12VDC rail. That's truth in labeling.  The only time I see these "common" misleading PSU specs is when I come across cheap POS Chinese units.  You buy garbage, you get garbage.




Here are some el cheapo PSUs with misleading specs:
1). $15 480W PSU with 330W continuous
 2).  $25 550W PSU with 460W continuous
I don't mind seeing this type of "inflated labeling" on a $400 Wally World Special.  But when a customer fork over $2.5K on a PC, then I expect the manufacturer to be more "honest" about the advertised spec.  The PSU is one of the most important component in a PC.  There is no excuse for slapping a "value" 380 watter on a $2.5K PC!
Message Edited by RoyalSerpent on 04-06-2009 07:56 PM
Posts: 13
Member Since: ‎03-01-2009
Message 9 of 499 (69,653 Views)

Re: Guide for Selecting a Power Supply

WOW! Thanks for the great data! To answer your question my computer has a core 2 duo processor rated at 3.0 Ghz. I hate to admit it but I don't remember the exact processor model.


The info I got from Nvidia was just an answer to my generic question "how much power does your 1 gig video card draw"? I did send questions to several of the PSU manufacturers. The two that answered told me I needed from 800 watts to 1,000 watts PSU.


The d5200 also uses a HP Pocket Media Drive 360 GB. I doubt it draws much power. However, this computer comes with the cables to add two more SATA hard drives and it has three bays in the upper tower for extra DVD burner(s) or floppy drive(s) or whatever. Since the architecture of this computer is intended to be expandable by the user I believe the installation of a 385 watt PSU is quite small and it could not possibly have any power reserve for optional devices that are intended to be added.


This disapoints me as much as the new TiVo TV tuner cards. That is cards with an (s). This came with the best TV HP offers. They install two TV tuner cards in the machine. New from the factory I checked the device manager and found a conflict between the TV tuner cards. After 11 hours on tech service and three recoveries completed the problem is not solved. When tech service does not have an answer they insist you do a recovery. This new computer with all the bells and whistles leaves me quite weary.


I was never able to get tech service to understand that since the computer was new out of the box the recovery would not have anything to recover. Finally they admitted they are not trained in TV's. I am glad they took the time to attempt to help me. However, it would have been better since the tuner conflict is a known issue they handed the call to someone skilled in this area.


Today I had a case manager call me and he kept telling me he wanted to buy it back. I bought HP because I like HP. This is a replacement for my HP d5000t that they sent for repair three times and instead of installing new hard drives (RAID1) because or SMART error codes, they did a recovery each time. One this one I will stick up for the case managers. They told the repair department to replace the hard drives due to error codes every time I started the computer. The repair folks ignored the case managers orders three times in a row and they gave me a new computer. I do believe the repair folks are a contracted outfit. I was unable to exert any influence over the repairs. So this is HP computer # 2 since October 2008.



Associate Professor
Posts: 1,250
Member Since: ‎01-27-2009
Message 10 of 499 (69,718 Views)

Re: Guide for Selecting a Power Supply

[ Edited ]

I'd jump on the buy-back offer.  I'm on the West coast.  It takes about 2 days to assemble and test the rig.  Per my previous post, the finished product cannot be subjected to high G loading during transport.  Anyone can buy parts.  The secret is final assembly and tuning/testing to achieve a fast and reliable PC.


It's very important to know exactly what you want to do with this PC.  I would only go with a quad core if you're going to encode movie.  Hold off on blue ray at this time.  Wait for the burn technology and media to mature before engaging.  I'm not a big fan of the Hauppauge unit.  The SiliconDust HDHomerun with dual digital HDTV comes with a very good receiver.  The dual tuner permits watching and recording at the same time.  It's not cheap at $160, but the technical support and hardware integrity is very good.


PSU manufacturers will tell you to buy the biggest PSU that they make cause there is a huge mark-up with those +800 watter monsters.  I rely on calibrated equipments to tell me how much power is being drawn from the AC outlet.  We know that the Intel spec is very accurate (135W).  Since each 6-pin GPU power plug is rated up to 75W, a GPU with dual power plug will not draw more than 150W.  A quality 500-500W PSU should provide ample room for future upgrade (single GPU rig).





Here's a quick run down on the quad core Intel rig:
Motherboard...$99 (3 yr warranty)
CPU...$230 (overclocked to +3.4GHz with 3 yr warranty)
CPU cooler...$37
8GB RAM...$82 (lifetime warranty)
Power supply...$70 (5 yr warranty)
Video card...$95 (3 yr warranty)
PC case...$60
DVD writer...$50
Hard drive (2 x 1TB)...$240 (5 yr warranty)
Fans and fan controllers...about $40
Card reader...$15
Windows XP Pro 64-bit...$140
Note that you will need 64-bit windows if you want to use more than 3GB of RAM.  The drawback is that some older applications may not work with 64-bit windows.  Final cost is $1158 + tax + $200 for assembly and system configuration.  You can expect to save an additional 17% if you purchase equivalent components when they go on sale. 
All else being equal, an AMD quad core will cost $100-$120 less than in Intel quad core rig.  Both will easily outperform any $2000 quad core rig sold at the local retailers.
I'd go with an overclocked E8400 @ +4.0GHz righ now.  This rig should be blazing-fast for the next 2-3 years.  By that time, you can swap out the MB, RAM, CPU, and GPU to take advantage of the latest PC architechture.
Message Edited by RoyalSerpent on 04-06-2009 11:52 PM
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