I had a similar issue - some hum was presenting itself via my DAC, and it got louder as I increased volume. I was able to get rid of it by removing the ground pin of the DAC's power cable (just as an "advance test" as the above poster mentioned). I then picked up a HumX, replaced the ground pin on the power cord, and plugged that power cord into the HumX (and the HumX into the wall). Works beautifully.
Note that the HumX has a current limit of 2 amps (I think).
Note that the HumX has a current limit of 2 amps (I think).