Something "rang a bell" with me, re. the 1600 series desks, so I just looked up the docs at the soundcraft.com website. In addition to +/- 18 VDC, that desk's power supply also provides:
+/- 7.5 VDC
+ 24 VDC
+ 48 VDC phantom
....all on a round 10-pin connector.
Thus, a replacement PSU will require multiple Power-One/International Power/Condor/whatever modules, beyond what is required for the audio rails.
I AM sort of surprised there is no fusing for the individual rails which would give a hint as to the current requirements, but a few rails can be guessed-at since they use 3-terminal regulators.
The 24V rail uses a LM-338 which has a max rating of 5 Amps.
The +/- 7.5 VDC rails use 317/337 regs, which are 1.5 Amp max parts per rail.
Phantom is a no-brainer since the abs-max that any input channel can pull is just a tad over 14 mA...IF mic input pins 1/2/3 are ALL shorted together. The smallest Power-One/whatever 48 VDC module is rated for 0.5 Amps, which means it can happily supply a 35 channel desk with EVERY mic input shorted across XLR pins 1/2/3.
As for the +/- 18 VDC rails, the required amperage for those two is unknown to me without doing some reverse engineering from the schematics. 4 Amps may or may not be enough......