I'd like to offer an alternative view than the ones stated above. I have owned the Hydra, the Power Plant 300, the Power Plant 600 (and currently still own the Hydra and a modified PP300). I do not agree that, in all instances, the Hydra "blows away" the Power Plant. For large draw components, such as amplifiers, the Power Plants are overly restrictive of dynamics, and seemed to subtly "white out" upper midrange textures. However, for source components, particularly digital sources and turntables, I found the Power Plants to provide a reduced noise floor, higher levels of resolution, and even tighter, more extended bass in comparison with the Hydra. For preamps, I generally found it to be a wash, depending on the component used. Thus, I am currently using a combination of the two in my system - Hydra on the amps, and PP on the sources. In any event, I strongly recommend you audition whatever power conditioner you plan on buying, if at all possible. For example, when I moved to my new loft in the city, the quality of my power from the wall went down dramatically, thus rendering the PP300 even more effetive in comparison to the Hydra.
I would also suggest, if your budget allows, checking out the Accuphase units and the Exact Power EP2000, which essentially are buck boost type regulators that output a clean 60 Hz.
