Turns out my pedal board's 9 volt feeds are 100ma max (more than enough for 99% of the 9 volt pedals). The MP's power supply is 200ma. Plugged in the supplied power supply and everything was fine. Oh well.
Is your board a Furman? My SPB-8 is 100ma so I had to use the Wal-Wart that came with the POG. The SPB-8's Boss-style connections would not give the POG enough power.