Originally Posted by Wired
Only thing I can think of is that if a UPS doesn't give true sin wave output (e.g. cheap quality), some PSUs may buzz a bit due to that, but that's it.
Just to clarify on the "buzz" mentioned above, it should only occur when the UPS has lost a/c power and is running on battery only. Furthermore a non-sine wave UPS does not necessarily indicate a cheap quality
UPS. IMO there is no reason to invest in a pure sine wave UPS for your average "home" computer, and Corsair reps have stated
that there are no ill effects of running off the battery (for a short time mind you) of a stepped/simulated sine wave UPS.
Should you be considering a UPS then I would recommend a line-interactive model at a bare minimum since they add some degree of voltage regulation. The off-line UPS is a low-cost product that protects primarily against a power outage. It is not a complete power protection solution. You can read more about them here