G4 17" Power adapter issues?

I've got a G4 17" Powerbook, loaded, that has been having an oddity with the power supply. When the 65w power adapter (the white square one, 2-piece) is connected it sometimes seems to ignore that there is an adapter and runs the battery down to zero. If I unplug the adapter from the computer and reconnect, nothing. However, if I disconnect the white DC box from the power cord and then reconnect the two, it fires right up and charges. This happens seemingly whenever it wants, no pattern. I swapped out another power unit.. same problem. Battery? Adapter? Other mess? Anyone heard of this before?