To make more progress, I'd suggest (assuming you have a desoldering gun) to remove the main transformer. Then check the transformer out of circuit (to verify all the windings!) , then with the hole that provides, you can access both sides of the PSU while they are exposed. This will give you better physical access and also remove the inductor at the end of circuit you're trying to isolate/check.
Quick update: I've been trying to familiarize myself with the board, looking for shorts, and tracing the circuit. So far nothing stands out as obviously shorted.
There are a few things that surprised me though:
The rectification seems to happen before the transformer lowers the voltage. Does that make any sense? I'm only familiar with much less sophisticated power supplies that first lower the AC voltage and then rectify it. This is my initial tracing of the circuit.

There's that nebulous area to the right that I haven't fully traced and it even corresponds to some of those cables that go to the other board (which I don't even know what they do there, since it goes into that coil-looking device with the red cylinder on top--any idea what that is?)
The part that makes sense is that the big capacitors (and the one that blew up C115) seem to be after the rectification, but before lowering the voltage, so that explains their ratings.
Is the primary transformer really the fragile-looking one to the right? The one that looks like a wad of bills rolled up?

Somehow I envisioned something much more robust looking for these kind of voltages, but I don't see anything else that could be the primary transformer.

But also, if that's the transformer, its output goes straight into that connector on the top right, which goes to another panel. A transformer only works on AC, so that must be getting the signal before it was getting rectified.
It's frustrating not being able to turn it on and follow the signals along! I don't imagine it would be a good idea to try powering it on (even with a current-limited source) without connecting it to the rest of the PSU, right?
Anyway, I'm out of time for this week, so I'll have to pick this up next week. Thanks again for all the help and insights!