I was getting a slight hum and occasional crackles through my speakers which I resolved by using a power supply filter unit (Nobsound Audio 3000W 15A Audio Power Purifier Filter AC Power Socket Conditioner). I am not sure at what stage the interference was introduced, but it turned out that the hum was the result of using powerline adaptors to connect my streaming-based system to my network. I resolved this properly by getting the house wired with ethernet cables (much easier than I thought it would be). Since we are subject to quite frequent power outages and surges, the Nobsound unit made sense anyway. The quality of the sound has not been improved, but interference has been eliminated.
Nonetheless, I agree with those who have pointed out that there are countless pages of meaningless debate over power cables, etc., to be found in hi-fi chatrooms. Personally, I doubt that you can improve quality, but you may be able to remove unwanted glitches.