Hmm from first link:
"Some wicked design idea back then mixed up the wire colorings: the standards tell (what you can except from the PC fan as well) that the red wire carries the positive voltage, while the black is the ground. Here although the black wire is properly attached to ground, the red is not carrying the voltage. Carefully examining the board will reveal that the red and the black wires share the same voltage (0V). The power (16.5V) is carried by the yellow (!) wire. "
So the 3 pins are Gnd, Gnd and +16.5v. Using a ohm meter you should be able to find which pins are ground checking each pin to the metal back. Those of 0 ohm be ground, the one with higher resistance should be the +V
https://macdat.net/images/laptops/chicony/nb5620/back.jpg

Thanks for reading more thoroughly than I did!

Tested with a meter and added a markup for future reference. Looking at the back, the top pin and right pin are ground, and also have continuity with the metal back plate. That leaves the pin on the left to be the voltage pin, but I'll find out when I get some sockets that hopefully fit.

And a few hours of fiddling later, we have a plug! Thanks again!

thingsforjason wrote on 2025-05-15, 15:59:

And a few hours of fiddling later, we have a plug! Thanks again!

Nice, that's 3d printed? Did you use springs for the contacts? that should have a really good contact surface.

To do similar with mine I've used some gold plated 2-leg socket pins which are wrapped in heatshrink then placed onto the pins. To make the shape of the connector I melt down some black thermoplastic (blackmorph) pellets on the hotplate and then jam that plastic into the connector, pushing it in so it doesn't get airgaps. That's my quick way to make weird connectors since the heatshrink stops the plastic going into the pins that matter and once cooled, the connector usually comes out without sticking to the DC jack and the molded version has the keying features 😀

I harvested those socket pins off of a dead industrial PC board that used 3 or 4 row 2.54mm board-to-board connectors, taking the pins out from the female connector. Apparently that's called a DIN 41612 Connector, nice gold plated contacts on the female socket parts that's pretty good for making bespoke DC jacks with.