Today I leafed through a folder of Jung (manufacturer of wall sockets, switches, etc) and saw they now have a
wall socket with 2 USB outlets, there's also one with a single USB outlet. As far as I know Jung is available in Holland and Germany, I don't know about other countries.
I'm going to see if I can get my father to order one and put it in one of the displays, I think people might be interested in it since more electronics can be charges with USB.