My PS Audio P-10, $3000 used approx. regenerator has a screen showing about 3% distortion and 118.5 volts which it reduces to .1% distortion @ 120.1 V. I can hear the difference and it's worth it to me (I have two.). Because this is a high price to find out, I suggest you borrow one from a friend as I did (they're heavy)-make an appeal here on audiogon- see if you can hear the difference and then ask yourself if it's worth it to you to buy one. Else, I think there is a trial period. While I realize this is a long winded way to say "try it before you buy it...YMMV" it's not at all intuitive otherwise: I live in the Atl. suburbs, a friend in the city has cleaner power! ; a friend in my same neighborhood even has cleaner power (closer to the transformer?). And so, even if you had a cheap, easy way to measure, what would the number mean? You still have to be able to hear a difference (there probably would be some, in any case) and decide if it's significant to you.
Analyzing the power from the outlet
I've been reading threads on the various methods of power cleaning -- filters, regenerators, dedicated lines, etc. But I don't see a thread that explains a systematic way of evaluating the condition of the power at the outlet. Is there a thread or a link that instructs on how to analyze the power for noise, voltage consistency, etc from the point of view of an audiophile?