Why don't you just copy the schematic out from the board ?
I have done this many times, for the entire 5155 power supply, entire VDU's. It is not that difficult.
In the end, a lot of vintage computer stuff was not well documented, so we have to do it ourselves.
Firstly, copy out the schematics and make neat error free copies. Then study the design and write up the operating theory. Create the topographical component layout with component designators. Then take scope recordings of the important waveforms and put together a "service manual" for the item and put it online. This way it benefits everybody.
We either value these historical items enough to put in the work, or we don't, or they go in the rubbish to be replaced by a modern supply, but I'd hardly call that "vintage computing".
It needs to be done to a good standard, here is the 5155 SMPS manual I created as one example, only about 21 pages required:
www.worldphaco.com/uploads/The_IBM_5155_POWER_SUPPLY.pdf
Unfortunately I don't have or own an ADM supply like this (or I probably would have already created a manual in the absence of one).
I could do it on a special request as a paid job for some particular SMPS, but it would have to be shipped to me in Australia. Ideally though I would like to see others putting in the effort when there is no manufacturer data. It would probably end up as about a 20 page manual.
Another example of boards where there is no data in many cases is motor control boards , the control board in my Sieg C1 mini-lathe was like this, so I completely reverse engineered it and wrote a paper on its interesting operating theory (largely done with OP amps) and it turned into a 46 page manual, but with it, the board now documented, can always be diagnosed and easily repaired. Before this people were making stab in the dark repairs (the usual global re-capping) and mostly failing:
www.worldphaco.com/uploads/THE%20ORIGINAL%20SIEG%20C1%20MINI.pdf
And other recently, the Taylor-Wilson PET printer interface which contained over 25 IC's and again no manufacturer manual or data, requiring complete reverse engineering of the pcb, the schematic from that and creating the operating theory which turned into a 37 page manual:
It all really depends on how much you value and like the item, to put in the required work.
For many people looking for a quick fix, making the manual may not be the answer. But not having it can be equally, if not more, frustrating. A wise individual said to me once: "Never get into bed with an item of equipment without the manual".
