Why does my 2017 iMac work in every building except my office building?
You can plug the Mac into any voltage from 100 - 240v &amp; it will not care at all, so that's a red herring. 

I'd suggest a mains socket tester plug, to ensure the socket is correctly wired, from the wall &amp; also the UPS.
Also, skip the UPS &amp; test the Mac directly in the wall too. That would be the most probable fail point.