One or two other things I noticed with regards to power and sound quality...
I recently had the power coming into my house from the pole redone. We had a pole in front of the neighbors house rot out at the bottom and it had to be replaced. As part of the work ticket from PGandE, the main from the pole had to be rerouted to a point closer to our house. A new pole and line was put in and service restored.
After everything was completed by the power company and my power restored, I hooked the sound system back up. I did notice an overall improvement in the sound. I was not looking for an improvement, just looking forward to listening to my system again. When I got powered up, it all seemed more cohesive and defined immediately. At the time I did not have anything but OEM power cables. I have always used power suppression and a UPS for power drops. Since then I have changed some of my power cables. Some made a noticable difference in sound, some just look cool.
Which brings me to another power related story that may be of interest.
A friend has a wood shop with some high power power tools. One has a 50 hp electric motor. When the motor was turned on, the power cable to the building would whip between the building and the pole! Most people would need to witness this to believe it, but it did happen.
The shop was near the ocean and salt water. The cause was the top of the cable insulation was compromised enough to allow moisture into the copper core and the top of the wire was oxidized, the bottom was not. This created higher resistance on the top of the cable and when high current was drawn through the cable, the dissimilar resistance actually would pull on the top of the cable. There are many power cables to houses that have this problem. They just dont have a 50 hp electric motor to show it. But, It probably does affect the sound of their system.