I appreciate the replies, but they still don't explain the apparent affect on the sound of a system. Once plugged into a wall socket, the power cable acts simply as a continuation of the power path from generation to your component's power supply (transformer etc); it isn't a discrete separate circuit as you suggest, in the way a power conditioner or UPS would be. It can therefore at best cause no further degredation to the power supply, but even a decent inexpensive cable will impart little to those two or three last feet.
As for RF/EM interference... yes, they exist and are a problem for low level signals in interconnects. But shielding less than 1% of your power supply chain is a bit like putting sunscreen on one finger and expecting the rest of your body to not get sunburnt.
I'm not trying to cause trouble here; I really am after some genuine evidence. But everytime I read "I spent $1000 on a power cord and Wow!", it sounds like "I spent $1000 on a power cord and it sounds no different but I don't want to admit I got conned by the HiFi shop."
As for RF/EM interference... yes, they exist and are a problem for low level signals in interconnects. But shielding less than 1% of your power supply chain is a bit like putting sunscreen on one finger and expecting the rest of your body to not get sunburnt.
I'm not trying to cause trouble here; I really am after some genuine evidence. But everytime I read "I spent $1000 on a power cord and Wow!", it sounds like "I spent $1000 on a power cord and it sounds no different but I don't want to admit I got conned by the HiFi shop."