I'm considering adding a second Radeon RX 7900 XT to my system for running larger AI models locally. My current setup is a Corsair RM850x 850W power supply, one RX 7900 XT, and a Ryzen 7 5800X3D. Would the 850W unit safely handle both graphics cards? My motherboard is an ASUS TUF Gaming X570-Plus, with the primary PCIe 4.0 slot running at x16 and the second full-length slot limited to x4. Gaming would use only the primary GPU; the second card would mainly be for AI workloads.
3 Answers
If the goal is larger local AI models, the second card can make sense, but the power supply and airflow need attention. Two 7900 XTs produce substantial heat and may draw close to the capacity of an 850W unit under sustained load, so a good 1000W–1200W PSU and strong case ventilation would be a more comfortable setup.
I wouldn’t use an 850W unit for two 7900 XTs. A quality 1000W PSU would be the safer minimum, with some extra headroom for transient power spikes and the rest of the system. Also verify that the PSU has enough separate PCIe power connectors—typically four 8-pin connections for the GPUs, in addition to the CPU power connections.
The motherboard’s second slot running at PCIe x4 will not be ideal for a GPU that needs to exchange lots of data with the CPU, but it can still be useful for compute workloads where most of the model stays in the second card’s VRAM. It won’t combine the cards into one gaming GPU, and most games won’t benefit from having both installed. For AI, whether x4 is acceptable depends on how often the workload transfers data between system memory and the card.
Since the second card is mainly for AI rather than gaming, x4 may be workable, but expect reduced transfer performance compared with an x8 or x16 slot. Check that the physical slot has enough clearance and that the motherboard and software support the multi-GPU setup you plan to use.
Make sure to check the exact connector layout on the RM850x rather than assuming every modular port can be used for GPU power. Avoid powering a high-load card through a single daisy-chained cable if separate cables are available.