All these people having PSU issues in this thread, it's like they've never built a system using 300 watt stock tbp gpus before.

How to size PSUs:

Step 1 - Add up the stock power of all of your gpus.

Step 2 - Divide by 0.8 so that if your OCs get reset and you don't notice you've sized to pull no more than 80% of the psu's rated power.

Step 3 - Take the combined power of your power supplies and make sure your wall socket can provide 15-25% more power than that without tripping the breaker.

Example:

You want a system with a cheap mobo + 4 Radeon VII gpus.

Step 1 - Power Draw = 60 watts (mobo) + 300 watts (gpu) x 4 = 1260 watts

Step 2 - 1260 / 0.8 = 1575 watts, or we need a PSU rated for 1600 watts or higher.

Step 3 - 1600 watts power draw * 1.25 = 2000 watts.  2000 watts / 110vac (rms) = 18 amps, or you need a 20 amp breaker dedicated to just this 1600 watt psu, powering just four Radeon VII gpus.


You really don't want to be maxing your psus out anyway for efficiency sake, you're burning more power by not running closer to the peak of the psu's efficiency curve.
https://i.imgur.com/wBkTB9S.jpg



On another topic, I've found that for ethash the point at which the gpu core no longer bottlenecks the memory on this gpu to be when the gpu clock is about 1.8-1.83x the memory clock.  Or 1800mhz core for 1000mhz mem, or 1620mhz for 900mhz mem.  Is everyone seeing similar in their fiddling?