If I were you, I'd look into the APC Power Centers. Not only do they utilize Isolated Filters to clean the incoming power signal, but they also have a Transformer so they can perform AVR (Automatic Votlage Regulation).
This way the incoming power can flucuate between 90-135v, and it'll always output a stable +/-5% 120v to your equipment.
The H series APC power centers have the transfomer/filtering. The J series have the same, but also include a battery, so it can also act as a UPS.
A great example of what a power conditioner fixes is when you run your vacuum, it'll show noise and perhaps distortion on the analog channels. Also, if you use any type of signal amplifier (like cable amplifier), it injects power into the line, and with it noise.
The APC H series run only about $350 and are worth every penny.
