Good power/Bad Power

Just a guess, but I think some electric utilities generate their power using low quality electrons. LOL ;<))

Hard to say how to tell if you do not hear any flaws.
Low voltage is easy to spot when a motor (like frig) kicks i and the lights dim..
Dimmers and other noise on the line? poor black levels/silence between notes. Same for TV, a HD TV can show a lot of grain in the background (over the air picture via antenna, Some cable co. the grain is their trash..)
Personally i do not think at your level a little flaw in the power is going to do a lot. Fixing it would cost too much for the little improvement.
The money would be better spend on better electronics.
Ditto fancy interconnects.. Why spend a lot on them when the money would do way more on basic components.
So stick with the cheaper solutions you have tried.
And save your money for music.

(one super cheap add on tweak is to place a 15 watt/25 watt light bulb in the wall duplex just before your equipment, or in the power strip, or whatever,,
So it acts as a 'buffer' it will suck up the 'noise' as good as any $50 noise harvester..
Whatever.. so it is just before the cords for the equipment
So use one outlet in the wall for your gear, and the other get a small plug in socket, or an ordinary lamp (no cord is best, so the plug in with the screw for a standard bulb)

Another worth while thing is to replace the old duplex in the wall with a $3 or so heavy duty Pass & seymour outlet from Menards. (Levitron totally SUCKS, so skip Home Depot!)

There's equipment that logs power data. It's not cheap stuff but its accurate.