I have tried searching for "amiga 1200 psu schematic" and many variations, but haven't been able to find an A1200 power supply schematic. I was able to find an A500 PSU KiCAD schematic and re-capping instructions for the A1200 PSU (though, this photo doesn't look identical to mine so maybe that's a PSU from a different region) but all other results seemed to turn up nothing that I could recognise as a schematic for the board.
The PSU has a UK plug.
I suspect a shorted cap but I haven't checked all of the caps yet. I believe a schematic would be useful to know what tracks should and should not have continuity. The line filter—at least, it looks like it could be the line filter—is damaged and I need to replace it, as well as the damaged 30 ohm resistor (above the word 'caution'). This damage was due to using an incorrect fuse (I have no excuse, the warning was right there). It seems the board is shorting, but I'm unable to determine why (it was shorting before the line filter and resistor were visibly damaged... I damaged them, oops).
Edit: Turns out 3 of the 4 diodes on the full bridge rectifier had shorted. I guess that there was a power surge causing a large reverse voltage. There was a thunderstorm recently. I'm surprised this is the only thing in the house that failed. It's a 1N4007, so the reverse voltage must have been above 1 kV.
The common reasons for a diode failure are excessive forward current and a large reverse voltage. Usually, large reverse voltage leads to a shorted diode while overcurrent makes it fail open.
I bought a new used PSU (which I suspect may have the same fate eventually), and I'm aware there are modern PSU alternatives for the A1200... but until it arrives, I thought I'd at least attempt to fix this board and get some (hopefully non-lethal) experience with mains voltage boards. I cut the wires to make it easier to work with. I'll probably end up using crimped connectors when (..if) I reconnect the wires.
Edit: There are also some burn marks on one of the jumper wires below the heatsink in the middle of the board. I believe a schematic would help me investigate that.
Edit: I actually probably won't use it once I've fixed it, since I'd indeed be worried about taking the computer with it as you mentioned.