Below is a shot of the original Power Supply board in question.

It brings AC voltages into the machine, rectifies and regulates it to deliver +5v, +12v and -5v to the motherboard.  A lot going on here, and no point in trying to replicate it.  As long as the replacement delivers the right voltages, with enough current capacity.

I have lots of 19vdc laptop power bricks around, with standard barrel jacks.  So, that's where I was going for a primary source of power.

Below is a shot of the pcb designed by my predecessors:

(Apologies for the quality).  I didn't use their exact circuit, but the board layout was dimensionally compatible with original in terms of size, mounting holes, and pcb footprints for the switch and output header that I would eventually steal from the old board.  It was therefore useful for designing my own PCB.