Well, I've been working on it over the weekend. Even with the old power supply. The ACA seems to be working for a while, then gets bored and gives up. I'm sometimes given a yellow screen, when it crashes and tries again.
I've tried it on a second 1200, and the same problem happens.
Amigakit haven't even bothered to respond to the email I sent.
As of this morning, I can't even get it to turn on correctly again. It's just giving me the blank screen again.