[phcorrigan]

When you say hum, are you talking about a 50/60Hz AC hum or something else? I've had AC hum with certain power supplies, and that can usually be attributed to the quality of filtering in the power supply itself. If the power supply has a grounded three-prong plug you may also be having ground loop issues, but in this case I suspect not.

I was having issues with my compressor/sustainer pedal giving me hissing issues, and I solved that with a noise reducer pedal, putting the compressor in the send/return loop of the noise reducer.

Overall, if you have no noise using a battery, then IMO, the problem is likely related to the power supply itself, and, although less likely, a possible ground loop.