On Monday, September 28, 2020 at 11:05:01 AM UTC+1, Roger Hayter wrote:
Snip

I think the secret is low current consumption. To drop (most of) 240V at,
say, 5mA needs only to dissipate 240 x 5 x 10^-3, that is about 1.2W and the
large resistor can probably do that even air cooled. Only few low power
components are needed to voltage limit, smooth and regulate the low voltage
supply. There should be an electrolytic capacitor though, unless anyone can
give a clue how to avoid it.

--
Roger Hayter

You are quite right Roger, I had forgotten there was a couple of small electrolytics near the input).

And thanks everyone, I shall probably never build anything like this, but it's interesting to know how they have powered what I presume is low voltage stuff.