Well I got some parts in and have the SCDR2 up and running - played some Rondo today (first time - it was great!)
But I've decided I can't live with using 2 ac adapters. This isn't a Sega CD...
I have tried a bunch of different adapters that I have, throughout the house, and none fit the jumper adapter jack. I even thought to try the Express/GT adapter...but nope, that's too small.
It's a weird size, in between the SCDR2/Duo main jack and the PCE jack.