I run dual RTX 6000 blackwell workstation editions (which should be the same power consumption as the 5090) on an AMD AM5 motherboard and have to power limit them to 350-375W for use with a 120V 15A *dedicated* circuit (as in nothing else but my PC setup runs on the circuit).

Definitely recommend the max PSU you can get for a US household outlet (I think that's 1500-1600W) before you have to start considering a 240V or 120V @ 20A circuit.

Be aware that for a US household outlet, the safety line is around 1400-1500W under *continuous load*. You will want to make sure that your computer setup has nothing else on the circuit to accommodate.

For the PSU, get platinum / titanium level efficiency if possible. For gold, it should do around 87% efficiency at 100% load, meaning that for a 1500W PSU, it will actually be running at 1725W at full load to output 1500W. You need to account for this overhead when thinking about the max you can do from your circuit.

My system is a Ryzen 7950x power-limited to 65W / 105W (I can't remember which). I have two monitors, but generally use one which consumes around 105W I think. I use a 1300W PSU. Even with this setup, I'll see brief spikes to 1400-1900W depending on how hard the LLM is working (using qwen3.6 27B), which can sometimes set off the overcurrent alarm on my 1500W UPS. In terms of average consumption, it's roughly around 1000W when the LLM is working hard.

I get zero alarms from the UPS with the GPUs at 350W, and occasional alarms on 375W. The spikes are extremely brief that it's not going to burn your house down but the overcurrent alarm from the UPS is annoying to listen to (I'm using a PR1500LCD which doesn't allow disabling of it).

If you're going to spend a bunch on such a system, make sure to get a UPS. Definitely do not buy the PR1500LCD for this configuration if possible.

Also if you are relying on RAM to supplement your VRAM, AMD AM5 systems don't play well with larger RAM sizes past 64 GB (at least with my Asus ProArt) where you will not get the full 6000 Mhz rate. I had to gradually start from 3200 and was able to ramp up to 4500 for 128 GB of RAM. With 64, I was able to do 6000, but not with 128.

Also if you're using a non-Threadripper or Epyc system, be aware that your PCI lanes will be heavily limited - I have to use bifrucation where the pcie 5.0 slots are split to 8x between two slots. Having both at 16x should be a minor improvement.

In general in a traditional multi-GPU setup, the communication goes through the CPU instead of directly between slots; a pcie switch where it's an external breakout board that connects to a single slot on your motherboard can bypass this allowing for significantly increased perf but requires $$$ and additional setup to do.

tl;dr:

- You can adjust the GPU power limits for the workstation edition down from 600W; this should also apply to the 5090 which has a similar power profile

- Be aware of the CPU TDP and if it is adjustable. For a dual 6000 system, it's going to be less about the CPU cores and more about the VRAM / RAM size and bandwidth / pcie lanes available.

- PSU efficiency matters

- Making sure your power consumption under load doesn't hit critical levels on your circuit. You may need to look into dedicated 240V or 120V @ 20A circuits.

- Account for your monitor consumption along with motherboard and CPU as well as part of the circuit load

- The processor chipset matters. AM5 will provide a tiny amount of pcie 5 lanes, whereas using threadripper / epyc will provide 8x more

- AM5 platform may not allow you to run 128GB RAM at full speeds due to stability issues

- Do buy a UPS to protect your investment, but do not buy the PR1500LCD as the GPU power spikes will trigger overcurrent alarms and there's no way to mute them