While dumpster diving the electronic scrap I find always interesting parts.
Last week I found some rack server with hot swap power supply. I removed the power supplies and reverse engineered the pinout of them.
On the following pictures you see the power supply and their pinout.
At the moment there are only the power and power-on pins known. The other unknown pins could be SPI or I2C for handling status information of the power supply or to regulate the cooling fan speed.
The power-on pins are often the shorter pins. They have to be shorter, because if the power supply is hot plugged, they should connect last after all other pins are already connected.
Power Supply Emerson 7001540-J000
3.36V STBY 0.45A
Power Supply HP DPS-460EB A
12V STBY 2.5A
Power Supply HP DPS-750RB A
+12V STBY 2.5A
Power Supply Supermicro PWS-1K21P-1R
+5V STBY 4A