NVIDIA A100 (SXM4 → PCIe) won’t POST when both 8-pin PSU cables connected - only works with one

Gaming and Visualization Technologies General Topics and Other SDKs GPU - Hardware
1

Hi all,

I’m building a workstation with an NVIDIA A100 80GB PCIe GPU - specifically, an SXM4-to-PCIe converted version - and running into a strange power-related POST issue. I’d love any insight from others who’ve worked with this card (especially SXM4 conversions) or with datacenter GPUs on consumer boards.

💻 System Specs:

  • Motherboard: ASUS ProArt Z790

  • CPU: Intel Core i9 (with iGPU - used for display)

  • PSU: Lian Li EDGE 1300W, 80+ Platinum

  • GPU: NVIDIA A100 80GB SXM4 converted to PCIe (PCIe bracket, 1× 8-pin power socket)

  • Cables: Using included adapter harness (dual-input to single 8-pin)

🧪 What works:

  • BIOS boots perfectly with no GPU

  • BIOS boots with A100 installed and only one 8-pin power cable connected

  • Display from motherboard HDMI works fine (BIOS set to iGPU, Above 4G enabled, Gen4 and Gen3 both tested)

What fails:

  • As soon as both PSU cables are connected to the adapter - system halts at white VGA Q-LED on motherboard. No POST, no display.

  • Tried multiple cable combinations, separate PCIe jacks on PSU, different slots - same result.

Suspected cause:

  • The adapter cable that came with the GPU has only 7 wires going into the 8-pin GPU-side plug: 3 yellow (12V) + 4 black (GND).

  • A full PCIe 8-pin should have 3× +12V and 5× GND. The 2 extra grounds are used for sense pins - likely the GPU detects that it’s not getting a complete connection and aborts startup.

What I’d like to know:

  • Has anyone else dealt with this issue using a converted A100?

  • Any BIOS tricks or power tricks that helped?

  • Anything I’m missing or anything else I should know?

Thanks

Josh

*I know - I’m building a consumer grade pc with a data center grade GPU, I’m clearly an idiot, but if you can spend a few minutes to help this idiot out I will be eternally grateful.