Thanks all for your kind help and pointers - it is very much appreciated and it is nice to find such a friendly forum!

To update, this evening I took the IIci apart, laid it all out on the table and used some cat-5 cabling (!) to connect up the PSU output pins to the corresponding inputs on the motherboard. I briefly connected up pins 9 and 10.....and the Mac booted up perfectly. Shut down, hotwire again, booted up perfectly, again and again. (By the way, the PSU is a GE not an Astec).

So, I'm guessing still capacitors....?

Many thanks!