I turned on my RiscPC and lo, “Thwooop” it went.
RISC OS 4.02
And then things went a bit wrong as it ran out of memory (it used to have 64ish meg, now I think it’s got 12 thanks to death-of-battery), but it made it to the desktop.
And then I discovered that like many modern LCD monitors, the one I’m borrowing to test things has little to no knowledge of ancient ‘puters. I think I may need a VGA to HDMI converter that’ll handle any input, because I suspect it’s switching to something like 50Hz 640×480, or some other hideous mode, and the monitor just cheerfully says “Mode not supported”.
After a few abortive attempts to play games I thought “ah, but what about Xenon 2! That might work”.
Still, the 115v mode on the power supply seems to work, there were no hot or burny smells, I think that one counts as a win.