One thing I am going to add to my dedicated outlet box is capacitors across the hot/neutral. See the following:
http://vhaudio.com/acpowerconditioning.html
....
They'll fail someday, you realise. Not immediately, but sooner or later a surge will take them out. They aren't rated for this use and caps can fail by going to an open short (I speak from experience). Do you have a fuse between the AC line and the cap? If not, you're betting the house on the circuit breaker's reaction time.
Filtering belongs downstream from fuses, unless you're certain the filter's failure mode isn't dangerous. In the case of a cap the manufacturer doesn't feel like certifying for AC line use, I don't think you have much assurance of that.
Anyway, unless I missed something, throwing a cap across a power line is going to do more than eat ripple - it's going to slightly reshape the sine wave. It shouldn't ever matter - but to be safe, don't decide it's ok to plug a power drill or other large motor into that line (not just the box, the line). The phrase "tank circuit" comes to mind. Make sure you are certain this can't be any sort of problem.
