You should not use the stereo plug. The tip and ring on the mono plug are the pos and neg of the power cable.
Make a trip to radio shack and get the right adapta-plug tips and an adapta-plug Y cable. The diagram on top of the ps-2 and ad-20 show if the tip needs to be pos or neg, and the cable and tip are clearly marked so you can see which way you connect it.
You can even get the female connector so you can plug the rc batt right into the cable.
JAson