I'm using Super Flower Leadex Titanium 1600W for my 2 overclocked S5s. 4 fans + 2 S5 @ 400MHz are drawing ~1350W from the wall thanks to the PSU-s extremely high efficiency. It also handles voltage drops without any effect to the miners. It happens in the area where miners are that voltage drops from 230V all the way down to 180V. So far miners were never affected.