Well, the job of a power amplifier’s PSU is AC to DC conversion, so will it matter if the quality of the incoming AC is less than optimal? Will a power amp’s PSU correct an irregular sine waveshape (indicating baseband distortion) before the AC-DC conversion? Unlikely. The important question is - does it matter?
As to horrendous electricity, does anyone without an AC line harmonic distortion analyzer really know how bad their electricity is? If I believe my P15, my AC feed to it, from a power subsystem in a perfectly normal upper middle class 25 year old neighborhood, is showing 4% distortion. Is that enough to matter to audio? I honestly don’t know. Does my system sound better with my source gear plugged into the P15 as opposed to my RSA Haley? Yes, it would seem so.