I suspect because of the 'very limited space' to which I previously referred.Just got off the phone to MK Tech. The USB ports built into 1363 socket plates are always on ...
As you say, it would be interesting to know how they've done it (safely)!... but the euromod USB PSU (which is the one I need) is activated upon insertion of a USB plug. How, I dunno...but I'd like to be able to afford a unit to teardown!!
Kind Regards, John