Is the preamp working properly? Does it sound fine? If so, don't worry about it. The wire doesn't care. Most commentators didn't know it was a wire between an outboard power supply and the preamp. So it IS supplying DC. All power cords going into the wall sockets, all interconnects and speaker wires are carrying AC and the current is reversing at many frequencies all the time. Unless someone is playing tricks with sheilding (some only ground one end in special situations) the directionality of wire is a myth.
