Actually, when I started breeding snakes over 20 years ago, I saw the term and asked about it by snake breeders who had a lot more experience then I and was told that power feeding was when you feed more then you normally would for maintence in order to get the snake to grow faster. A pretty open ended definition if you ask me,.
I don't think I've ever actually met anybody who claimed to power feed by stuffing rodents in their mouths one after the other after the other so the snake ends up swallowing more then it would have. The only time I ever heard of something like that it was being recommended as a way to get weight back on a seriously skinny snake and I think it was called train feeding or something like that.