I have personally never seen the issue (what caused it) but I did have a look at another one from a shop that brings me stuff they can't fix in hopes that I can fix it. Lol.
This one had some very slight water damage probably like 1 drop next to the charge port connector.
Anyways I took a quick look in a 2 day period I could not find the cause.
Everything checked out.
I changed out the sketchy looking capacitors.
I even changed the tristar and still same issue. Would not charge.
Good luck maybe if I have more time with one in the future I may be able to figure it out.