Looking for reliable pin-out of a HP DPS-750RB (or similar) server power supply

[neo2001]

I have a few of those, mostly to power chargers. Since these devices are commonly used for this, there are a bunch of tutorials and howtos out there. But basically all of them only tell you to put a resistor between certain pins to power the device one (similar to a ATX power supply). But what I'm looking for is a more detailed description of the pins exposed on the back of these devices (like those in my attached image).

As far as I know, this format is called CS or "common slot", but there seem to be different versions with different numbers of pins.

For example some put a resistor in between two certain pins, some use a bridge. Some descriptions say to pull down the PSON pin to GND (which doesn't do anything on my device). But connecting the outermost to the shorter pin does the trick for me. Still, I'm not sure what exactly I have connected now. I measured if there is any current flowing between them and since there was virtually none, I just used a wire to bridge them. One of the pin delivers 12 V standby voltage, another one 3,3 V and one 2,5 V. Now I wanted to add a LED to signal standby state, but don't want to use 12 V standby for that. But I'm not sure which other pin I could use for that. It would be really helpful to have some kind of pin-out or datasheet for this. But unfortunately unlike ATX this doesn't seem to be publicly available(?).

Does anyone here know more about this standard?

[neo2001]

This is what I found out:

The resistor that most people use between the PRESENT pin and the PSON pin is basically just a hack.

To allow for the the device to turn on, the PRESENT pin must be pulled up, for example with a 22 k\$\Omega\$ to the 12 V standby voltage.

Then (and only then) connecting the PSON pin to ground will actually turn on the device.

The "hack" resistor seems to pull up PRESENT and to pull down PSON at the same time and at a certain resistance value.

[NiHaoMike]

Some other attempts to hack those PSUs:
https://colintd.blogspot.com/search/label/HP%20Common%20Slot
https://github.com/raplin/DPS-1200FB
https://github.com/slundell/dps_charger

I have hacked one into a 4S lithium charger, at this point it sort of works but runs hotter than I like when the battery is close to full charge. It would probably be better to hack it to charge a 3S lithium pack (just need to add a current limit circuit) or 12V lead acid or 4S LiFePO4, since in my experience it's when the voltage goes above 15V or so it starts heating up.