Thanks everybody. It's definitely AC then. I\m looking at this replacement:
https://www.drench.co.uk/p/hib-turbo-cool-led-inline-chrome-ceiling-fan
It seems to be high quality. I just need the unit though and not the fixing kit. And it doesn't say what the power supply is. Chatting to their...
It might be related to this thread which has just shown up as a similar thread.
https://www.diynot.com/diy/threads/measuring-transformer-voltage.220417/
Photo of the transformer attached - looks DC to me
I have an ageing extractor fan above a shower that goes into the loft. It has a two pin centre bulb which only comes on when the extractor is switched on. That continues to work. I thought I'd use a multimeter to check the DC power output in the transformer in the loft and can't work out why it...