[oudplayer]

Depends on many things. If you have an always-online UPS which outputs a constant sine-wave 120v signal (and always runs off of batteries), you benefit from a lot more of filtering of the power of the type claimed by rack-mount furman units and the like. They can be had fairly cheap from ebay, but cost around $500 and up new (depending on the size you need). We run two 10 amp ones on a dedicated circuit in our studio, a studio in an industrial building with very unclean power, and they are very effective tools for combating power fluctuations and the noisy building power. For our situation, it provides as much noise reduction in our system as the Equitech we have running on another circuit. But your electrical system may have different needs.