Martin Brown wrote:

And sometimes annoying not marked at all on either part. It would have
been nice if there had been a manufacturers convention on polarity and
external diameter used for a given voltage, but it is pretty much
random. Centre positive is more common but there are exceptions

Cor, where you been living for 10 years? (I'm going to get bored of this
but not before you lot are.) Remembering the days of them being a
hotch-potch of polarities, I always check any switched mode wallwarts
that come my way amd I've not found a PSU with a negative centre pin for
years, probably not since the days of having actual transformers in them.

--
Scott

Where are we going and why am I in this handbasket?