powering multiple digital pedals

[tempus]

Hey all;

My board has a Zoom G2Nu, Zoom A2, Boss CS2 and a Boss NS2. I've been trying to set things up so that I can use a single power supply for all of these pedals, but they don't seem to care much for my idea. The 2 Zoom pedals are basically small multi FX units; the G2Nus uses a 500mA switching adaptor, and the A2 uses a 300 mA wall wart type. They're all 9v, centre negative pretty standard stuff.

Which is why I can't figure out why I can't get a single power supply to power them all (as opposed to a bunch of wall warts plugged into a power strip). The 2 Boss pedals are fine on 1 supply and they currently are along with the uP switching matrix inside my pedalboard. However, if I try to plug in either of the 2 Zoom pedals (even without the Boss pedals plugged in) I get weird behaviour and strange noises coming from them.

Is there something unique about digital FX that I'm unaware of that would cause my predicament? Do they need a dedicated supply or ground or something? Would one of RG's OneSpots work in this situation?

Thanks