On Tuesday, August 27, 2019 at 2:39:00 AM UTC-7, wrote:
I've also followed the advice to remove the remaining epoxy from the chip and
look at it under a magnifying glass (unfortunately I don't own a microscope).

I have uploaded some new images (viewed through the magnifying glass) to the
same link (the new pics are at the bottom):
https://imgur.com/a/uBCXjwQ

There seems to be no part numbers on the metal layers. I'm also not informed
enough to know whether it is "too complex to be a simple transistor and
complex enough to be a regulator, or something in between like a Darlington".
To my untrained eye it seems pretty simple, so maybe a transistor then?
To my eyes, it looks like there is no remaining silicon there at all (maybe it got destroyed explosively when it blew off the epoxy) and all you have left are the wire leads. The wires alone do not tell you much.

Can you trace out where the wires go? If it is a regulator, then the center lead will usually go directly to ground (nearly zero ohms to the negative output terminal). If it is a TL431, the left wire (looking at the flat surface with the wires down) will probably go to ground. And if it is a pass transistor, then probably none of the wires connect to the ground.