I've been enjoying these little wonders for about a month (look like large wall warts and are plugged into the same outlet as the component -- that is, you don't plug your PCs into the them). Basically, they clean up the HF and LF without covering anything up. In fact, dynamics increase and the overall sound is more natural and unforced.
Given that I have two dedicated outlets (one for source and one for amp) and an equi=tech balanced power unit just for the source, I was interested if the PEs could make any difference. Initially, I was interested in assisting the amp, which is plugged straight into the wall. Alan suggested trying three PEs, one for the amp, source and the equi=tech. What the hell, why not -- money back and all that.
I tried that and, with the exception of pulling them out to add them one at a time to see what each added to the overall sound, they have been in my system since. Great stuff. They need 10+ days for settling in. Very reasonable price for what they do. If you don't have the cash for several, I'd suggest starting with the digital outlet first. Alan was very helpful by explaining what they do, what to expect and what to use in my configuration. His website is a good place to start. Website:
http://alanmaherdesigns.com/default.aspxPhil