It is VERY hit or miss.Huh, well that's good to know, it's hard to get accurate info on specifics like that since ups waves aren't part of any reviews I can remember. It's seriously hit and miss. I know my Evga G2 550w absolutely does not like even stepped or modified square waves at all. I'm stuck with pure sinewave or nothing.
Honestly not sure what the UPS would do if fed a square wave from an inverter.Does it matter what waveform the inverter is? I guess not. Because during outage, the power from the inverter the power will go through the UPS to PSU and then to the PC.
It's a square wave inverter by the way.