I agree with audphile1 the biggest improvement I found was with my CD player which is Sony SCD-1 with a PS Audio Statement Extreme.The improvements were a lowered noise floor and a much blacker background. I have the same power cord on my amp and have not noticed much of an improvement. However, I did not experience a degredation in sound quality as audphile1 did. With my pre-amp no difference was experienced again utilizing the same cord. As a side note my Amp and Pre-amp already came with decent power cords with hospital grade ends so maybe that is why I did not experience much if any improvement. I did not experiment with differenct brands of cords so I can not comment on the impact a different brand might have. So in general your friend might be correct depending on the quality of cord your equipment came with.
Chuck
Chuck