I ordered an ASUS Radeon RX 7900 XTX 24GB OC graphics card for running LLMs with a Ryzen AI 370 mini PC through an OCuLink dock. My power supply is an MSI MAG A750BN, which has two PCIe 8-pin connectors, while the graphics card requires three separate PCIe 8-pin inputs. The PSU is only being used for the GPU, so the CPU/EPS connectors, PCIe 5.0 16-pin connector, and SATA outputs are otherwise unused. Is there a reliable way to use an EPS/CPU 8-pin connector or the PCIe 5.0 connector for the third GPU input, or should I replace the power supply?
2 Answers
A 12V-2x6 or PCIe 5.0 adapter that splits into two standard 6+2-pin PCIe plugs is a possible way to get the additional connectors, but only if the PSU's PCIe 5.0 output and total 12V capacity are rated for the load. Check the PSU manual and cable pinout carefully, and use a cable made specifically for that exact PSU. Do not use a generic EPS12V-to-PCIe adapter just because the plug fits: CPU and GPU cables are wired differently, and an incorrect cable can damage the hardware or trigger protection shutdowns.
The PCIe cable appears to have two daisy-chained 6+2-pin connectors, so you technically have two PCIe plugs available from that one cable. However, I would not consider this 750W unit an ideal match for a 7900 XTX. The card manufacturer recommends an 850W supply, and a higher-capacity PSU will generally include the proper number of PCIe cables. Replacing the PSU with a quality 850W or higher model that has three native PCIe connectors is the safest option.
Using two connectors from one daisy-chained cable may work, but the power supply's total output and cable arrangement are still concerns. I would avoid treating the unused CPU sockets as spare GPU power connectors.