So, if I understand your situation correctly, you have:
AMBrc
AMBrc power supply
System 20 rack
System 20 rack power supply (fried)
And you want to replace your fried System 20 charging rack power supply.
Out of curiosity, do you have System 20 transponders, or AMBrc transponders? I know the AMBrc system has a System 20 compatibility mode so you can use old software with it.
It's been a while since I've worked with a System 20 so I can't remember the details, but why can't you just buy another brick power supply for it? Do you not know the specifications?