After Market Power Cables - Gold or Snake Oil?

Myself and a collegue of mine have been discussing the potential benefit(s) of using after market power cables with hifi equipment. I claim that since the majority of home owners gain their power from the everyday wall socket, how does the addition of a short length of 'expensive' cabling make any appreciable difference to the sound quality. Are we kidding ourselves and buying into marketing hype or is there some scientific truth to the matter? I am a musician/recordist who understands the fundamentals of electricity and sound reproduction.