I just disassembled a Poweredge 1800 tower system to strip it for parts. It has a similar ATX supply, but 24 pins instead of 20. It is too old to be BTX, but it has the same connector, with the square pegs and alternating pairs of rounded pegs.
Pinout is roughly similar to this Dell layout with the addition of 2 blue/white cables, 1 blue cable and 1 black. Black is probably ground, blue are probably 3.3V lines, maybe + for the blue/white and - for the blue? Haven't gotten around to hooking it to a multimeter.
Hi iґm very intrested in having your results from that test
Could you check pinout for poweron reset and so on...