i have tried a russ andrews power cable in an a/b situation while working for a large music shop, i was very sceptical however there was a definite difference, subtle yes, better no, but different none the less, certainly not enough to warrant buying one or even considering it for that matter, especially considering the quality of the power outlets/supplys at a lot of venues where any upgrade would be pointless anyway.
i can undersand a hi-fi pureist using one a home with the perfect set up and an acoustically treated room but not for a gigging player.