Unplugging a component from the wall and plugging it back in often results in a noticeable degradation of sound, if you're paying attention to such things, until such time as the contact between the plug and the wall socket has a chance to "reestablish" itself, which can take a few days or longer. In fact, Disturbing cables or power cords in any way should be scrupulously avoided IMO, especially during tests.
Geoff
Geoff