It is a just a standard 12V/2A mains adaptor. I am measuring 12.4V with my multimeter.
I swapped the RX/TX around several times, so have definitely covered this. Also tested the USB to RS232 convertor with another device and this works.
As far as the LED is concerned, I have performed a factory reset and now the red LED is not persistent so I guess I had inadvertently set this to red previously 
Getting closer but still no serial comms.