Got a pair of these puppies from a friend who manages electrical supplies/equipment for local hospitals and were upgrading their equipment and getting rid of the old. Had to use a dolly to bring them into the house. They put out a constant 125 volts all day long. My wall voltage is around 119 volts. Haven’t done a blind test to compare if the music sounds better or not but I have no reason to believe they hurt the signal. They are basically large transformers - ILC Med Series.
http://www.tsipower.com/products/isolation-line-conditioners/indoor-isolation-line-conditioners