I heard two blind power cord demonstrations, where the two cords were both of similar price, and it was fairly easy to distinguish the cords in both cases, but whether or not one was better might be system and taste specific. In one of those bind auditions, I thought that a power cord by Basis Audio was clearly better (can't remember what it was competing with) because the sound was more dynamic and lively sounding. But, when I tried the cable in my own system, it sounded a bit too hard and brittle.
It is not necessarily a comparison between different price components; it is a matter of what sounds right. It also matters what component is being powered; I've tried different cords on some components where I've really not heard a difference. As a rough rule, tube gear, particularly linestages, seem to be somewhat insensitive to changes in the power cord. I don't think it is necessarily a matter of how much power the component draws either; I've heard differences with DACs that cannot be drawing that much power.