Now I just need to get the Ctrl keys on my keyboard working ... quite unrelated to the power supply issue, but I thought I wanted to clean it out, so I took it apart. I discovered that a) there was no need, and b) a Dremel is very handy for getting past recalcitrant screws. It went back together ok, and every key works except for both of the Ctrl keys. Guess I'll have to take it apart again, and with luck, not break any other keys.
Meanwhile, we have a suspicious damp patch on the lounge ceiling in the area under the small balcony of the flat above - I guess the faintly ridiculous amounts of rain we've had in the last few weeks has finally taken its toll.