Don't forget also that sound that is pleasing to the ear is not always "technically" better sound quality.
When we get into expensive AC power cords though we are going too far, in my opinion. They are not in the signal chain and therefore do not affect the audio quality, only, possibly removing 'clicks' from mains switches and the like.
Do recording studios use expensive "hi-fi" AC power cords?
Do recording studios use expensive "hi-fi" leads of any sort?