Since it was getting off topic, I'll continue here.
First off, I'm not picking a fight, merely clarifying.
__
There's no such thing as a 'pure' sine wave in UPSes even the 200,000 PKR APC ones (personally hooked it up to an oscilloscope). There is, but it closely resembles a simulated sine wave. It's a wee bit 'tighter' a voltage margin.
The reason why PSUs don't affect from simulated sine waves is because the voltage already has to drop down to a DC 12 5 and 3 V supply. That, and almost all PSUs are resistant to such ups and downs. The sine wave element of a UPS will only come into play when it's on battery power. There're a lot of experiments on the net. I'll share a few with you after I'm done with my exam on 2nd Jun.