Way back quite a few years ago I had a Sunfire true subwoofer that added more than just extra bass.
When I unplugged it from the wall and out of the system, the music was much easier to listen to and it seemed as if there was less distortion to the music.
My friend is an electrical engineer and he brought over one of his tools of the trade and sure enough that Sunfire sub was spewing all sorts of nasty spikes into the system.
Taking it out of the link and out of the wall plug, and the print out was more clean.
So, that brings us to just how much noise and "bad" things are poluting our audio systems that unless you see it on a print out, you'll never know is there.
But it is there all day, 24/7, just less when most people are asleep, hence the "system sounds better late at nite" syndrom.
I run my class D power amps into a Shunyata Hydra 2, using Annaconda power cords all around and into a dedicated 30 amp,line.
I run all my source gear into a Furman balanced power condition, IT 1220(20 amp)from another dedicated 20 amp line, both on the same phase at the panel.
There is absolutely no noise, hiss, hum , buzz, or snap crackle or pop from my system and it sound as good during the day as it does at nite(well maybe not quite as good).
The best way I have found to find out if you need to do some kind of power conditioning is to try some of the good ones(yes the expensive ones, not the power bar, computer type spike suppressors)have a listen, then go back to wallplugging and have a listen, and then put the power conditoner in for a final listen.
You only know how much the PC's are doing ,when you take them out and then re-insert them.
Personally, my system has never sounded so good until I took care of the power going into my gear.
Next to doing something about room taming,getting the power"cleaned up" to my gear has made more of a noticeable improvement than any recent interconnect or speaker wire changes have.
As noted elsewhere,cheap power conditoners on amps that they were not designed for has given all power conditioning a bad rap.
Bryston never subscribed to using a power conditioner on any of their amps, but now endorse the Torus line.
Yes they sell Torus,but until it came along nothing really worked on their amps.