On Sat, 11 Jul 2015 12:14:27 +0000 (UTC), Cursitor Doom
wrote:

Hi all,

Just before I connected up the PSU to this AOR comms rx I'd bought, I
thought I'd best double check the polarity was right, because someone for
some reason had spliced the cable at some time and put a new plug on it.
ON checking, I noted that though the polarity was correct, this psu was
putting out 19.33V - whereas it's rated output was stated as 12V!
This is not some cheap Chinese psu; it's the original AOR Japanese psu
made by them (or at least badged by them) for this receiver. What could
cause it to go from 12 to more than 19V? Don't these wall-wart style
supplies have over-voltage protection/crowbars, FFS??

Just curious...
Some supplies will not regulate voltage without a load. Try measuring
it again with a small load (eg, a 1K resistor) across the supply.