Incidentally, I built a PSU for my PC-jr last week. I used a simple 15V AC transformer, no centre tap or anything like that. The only one I could find was 50VA, which is marginal, but not too bad. The ends of the secondary go to the outside 2 pins of the PC-jr power connector. The central pin goes to mains earth and to nothing on the secondary side at all. Oh, I put a 3.15A fuse in series with the secondary to protect the transformer. It works fine. My PC-jr boots, and all PSU outputs (including the -ve one) are present and correct. -tony