PS-2 is power supply for mics (phantom power) they run on 9v disposable or outboard power supply. You can power it off the same battery pack as the one you build for the AD-20. You do not need this unless your mics are phantom powered. The battery pack is real easy to build infact it is almost imposible to do it wrong. When you go to radio shack this is what you need
1. RC 9.6v battery and charger ( they come together in a package for $20)
2. RC car repair kit (this costs like $5 and has the conector you will need to make your power cable)
3. Power cable (this is a cable that has a conector at one end that you can plug the conector that will go int the ad-20) This is a $2 cable that is designed to work with all the various power adapters.
4. mono 1/8" mini plug adapter (this is a piece that has a mono plug on one end and two prongs on the other) it will plug into one end of the power cable.
In the RC car repair pack is the piece you will need to make the cable. It is the same plug that is on the end of the charger. The plug has solderless conectors so all you need to do is strip the insulation off the wires of you power cable and crimp them to the plug. Now you stick the mono 1/8 mini adapter into the other end of the power cable and you done. Charge up the battery connect it to the power cable and plug it into the AD-20. If the AD-20 does not turn on you have the 1/8 mini plug in backwards take it out and turn it around. This may sound a bit complicated, but it is not. email me at wp420247@aol.com and I will send you some pictures. Also check out this. This is the same battery pack that you can buildfor $25 that micsupply sell for 50 bucks.
http://www.micsupply.com/ad20power.htmPeace, Matt