Update 2022-07-04: I read up quite a bit on pure sine wave UPSs and bought one and so far so good. The whole problem may not have been about grounding but about the garbage sine wave produced by non-sine wave UPSs. I have another compute running on non-sine UPSs so I'll try to report back comparing that computer to the sine wave computer.
Update 2022-05-21: The main problem I was trying to address here was random 'ups dop outs' even under low wattage usage by the pc causing the pc to reboot. As I understand it, some pc power supplies might not like artificial sine wave UPS power: So, my next test will be with a true sine wave UPS. Will update when I've run with one for a while.
Is there any way to use a UPS properly when there's no ground wire in the outlet?
I have a GFCI setup and an outlet with a ground wire but it's not a real ground (apparently; I don't quite understand GFCI). My UPS's that have a 'wiring fault' light indicate a wiring fault (lit up).
My UPS's will sometimes give out (and my computers will reboot), even on low wattage load (like less than 50%), and I suspect it's due to not having proper ground. But they give out even when there's no apparent surge/brown out, no thunderstorm, etc. Should that be happening? Would this not happen if the outlet were properly grounded in a modern way?