Did y'all mean to say milliseconds, and not microseconds? Sub-millisecond power loss would be less time than one AC cycle, whether 50 or 60 Hz.

Anyway, I do recall seeing some enterprise gear specifying operation through a drop in AC power lasting two cycles, precisely to cover the switch to UPS power, at least for 60 Hz power. So up to 33 milliseconds. A cursory search for hybrid inverters online shows a GroWatt with "<20ms" switchover, so this may be fine for servers and switches, when the inverter is operated without any solar panels.

For consumer grade equipment, all bets are off; some cheaper switch-mode power supplies do very weird things under transient conditions.