I'm looking to upgrade my graphics card but it says I need an 850 watt ps instead of the 750 I have

[Owendj]

I'm looking at getting a 3090 graphics card to replace my 2080 super and it says I need an 850 watt ps instead of the 750 that's in the pc so I'm wondering what power supply I should go with and if I can just plug the 3090 in and it'll work or what I might have to upgrade to get the 3090 to work in my pc

[itsmyname]

Is this your intended device:  https://www.nvidia.com/en-us/geforce/graphics-cards/30-series/rtx-3090/

That web-page states:

Graphics Card Power (W) 350
Required System Power (W) 750 -- see footnote
Supplementary Power Connectors 2x PCIe 8-pin
(adapter to 1x 12-pin included)

Footnote #4 - Requirement is made based on PC configured with an Intel Core i9-10900K processor.
A lower power-rating may work depending on system configuration.

Note: The above specifications represent this GPU as incorporated into NVIDIA's Founders Edition or reference graphics card design.
Clock specifications apply while gaming with medium to full GPU utilization.
Graphics card specifications may vary by add-in-card manufacturer.
Please refer to the add-in-card manufacturers' website for actual shipping specifications.

---------------

Of the 400 watts _not_ consumed by the graphics card, how much power is required for:

• your motherboard
• your processor
• any SSD (solid state device) -- much less power than any "spinning" disk-drive
• any CD/DVD
• power to USB ports

? 

Note that the 3090 is a "3-slot" device -- be sure that you have room to fit this device inside your computer.

[Prométhée]

Hi
not to mention the computer itself, available space, configuration etc.
Find a suitable model , depending on the manufacturer requirements may be different so you may not need to change the power supply.
for example

https://fr.msi.com/Graphics-Card/GeForce-RTX-3090-SUPRIM-24G/Specification

3 x 8 pin power connectors
Recommended power supply 850 W

https://storage-asset.msi.com/datasheet/vga/global/GeForce-RTX-3090-SUPRIM-24G.pdf

https://fr.msi.com/Graphics-Card/GeForce-RTX-3090-GAMING-X-TRIO-24G/Specification

https://storage-asset.msi.com/datasheet/vga/global/GeForce-RTX-3090-GAMING-X-TRIO-24G.pdf

Power connectors 8-pin x 3
Recommended PSU 750 W