RTX 4000 power connection in Z820

[earlyfilms]

I'm attempting to replace my K4000 graphics card with the RTX 4000 card, but I see the new card has an 8-pin connector while the old one has a 6 pin. I thought the reason the card came with a Y adapter (2 six-pin to one 8-pin), was to work as an adapter. When I power up, I get a message across the monitor "please power down and connect the pcie power cable for this graphics card".  I hope there is a workable solution for this.

[DGroves]

there is, read this link i strongly recommend the HP 6-8 pin adapter over no name cheap adapters

note the section where i talk about the GPU power rails on the upgraded power supply that has 3 gpu connectors

the stock 850 watt supply only has 2 GPU connectors (both on the same power rail)

read the section on Graphics and note the listed HP cards they are in descending order in performance/power draw and list either the 850 or 1250 watt supply pick the HP card that matches closest in wattage as yours (160 watts) which should be the AMD FirePro W7000 which is 150 watts as i recall and works with the 850 watt power supply

https://www8.hp.com/h20195/v2/getpdf.aspx/c04111526.pdf