Changing power cords is very efficacious for my Kingsound King III ESL speakers (reviewed for Dagogo.com), and in fact I tune the system partly by using different power cords with the ESL speakers' power supplies.
I had several people insist it would not change with power cord. I invited one repairer of Quads to come; he heard and admitted he was wrong.
Good point regarding outlets, maplegrovemusic.