I would like to emphasize the importance of Seans excellent description. My neigborhood has the first residential underground power distribution system dating from 1922. While the local utility has been piecemeal upgrading it, my power could be used as a textbook for anything and everything that could be wrong with AC. The PS Audio units are only ones that work for me. Taking a 'scope to your power source can help you decide what kind of power conditioner might help your system.
