Measure the short pads with a meter. One of them should be more than 3v. Ground it to turn the supply on. If not, grounding all 11 pins (one at a time) briefly shouldn't cause any problem.
Keep looking. Also check for information as to the server into which
it fits as that may reveal what you need.
Most of the similar power supplies that I've used (I built an electric
wheelbarrow using a pair of 12V 80A supplies) have a pin to short to GND,
often directly *opposite* a GND pin!
Note, also, that the case is often tied to GND (important if you need to
float the supply).
Reply by s7382●September 7, 20212021-09-07
https://i.stack.imgur.com/dJmy2.png
It has 3 long pads and 11 shorter pads, which to connect to power on? I can't find a pinout.