[update: added trace of pins]
I needed a chunky 12V power supply, and I have found one of these HS0550 which is rated to supply 12V @ 45.2A according to the spec;
It was surplus from an old HP StorageWorks XP20000 system. However none of the pins on the back seem to be giving +12V relative to what I think is GND. (there are pins with +3.6v and +4.68v)
Googling the product code suggests it's manufactured by Hitachi as a "HITACHI 5529219-A USP-V DKU POWER SUPPLY"; http://www.serverworlds.com/hitachi-5529219-a-usp-v-dku-power-supply/
Unfortunately, I can't find any docs on either the code 5529219-A or "HS0550"
I don't recognise the pinouts, but those connectors are actually adapters and can be removed, which gives 5 blocks of 6 pins;
I presume that these supplies use something similar to the ATX power supply standard, and require shorting across pins, or some other signal to enable to the 12V line; http://www.techpowerup.com/articles/other/22
But I can't find any explanation of what power standard this PSU is using...
Some general troubleshooting seems to suggest that the unit is working, as I can find 9v at some points on the board when powered up, and there is a test point which is reading something like 418v DC;
Here are some shots of the top and bottom of the board;
I've traced out the pins, and the brown trace looks like it should by the one carrying 12V. I think the blue trace is the signal for connection pin.
There are 3 opto couplers in the centre which I think are being used to switch on the main 12V circuit. 2 are connected to one daughter board, and then the other to a separate daughter board with the 12V level adjustment.