On Mon, 17 Jun 2013 00:25:24 +0000 (UTC), John
wrote:

I'm servicing an old PC switching PSU.
It's odd form factor and very small dimension prevents me to substitute the
inner board and forces me to repair...

I don't have much of a clue on how to fix that power supply. Too much
of the circuitry is under the black goo, and therefore impossible to
identify or easily replace.

If you supply some additional info, I think I find a suitable surplus
equivalent power supply:
What maker and model PC used this power supply?
Any maker or model number on the power supply case?
ITX? Mini ITX? Micro ATX? Mini ATX? Pico ITX? etc?
What are the dimensions of the power supply case?

Maybe:
http://www.mpja.com/Computer-Power-Supplies/products/36/
http://www.alltronics.com/cgi-bin/category/158
http://www.ebay.com/itm/160655942010

If you're totally stuck and can't find anything small enough to fit,
look into the various micro/pico power supply devices, where most of
the power supply is on the power plug, and is fed from an external 12V
regulated power source.
http://www.ebay.com/bhp/picopsu
If that will fit, you could use the space previously occupied by the
power supply case to install a 12V PS.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558