With a correctly designed power conditioner like a transformer based unit, which actually takes you off the grid, you are much better off plugging your amplifiers into the power conditioner.. This type of power conditioner does not limit dynamics at all, as long as you get the proper size transformer for your system. As a dealer, we have tried many power conditioners, but the ones that we sell are very effective.
That being said, if you live in the middle of nowhere, and have no electrical noise on your line, you can get very nice sound by plugging your amplifiers directly into the wall.