You obviously know more than I but the following may help.
I've always said it was an AC adapter for the reasons you've mentioned. In
this case it cuts the voltage from 230v down to 12v. It is powering the
decks DC motor. I also know what polarity it should be. My main concern
was
the "20mA" on the adapter. I have a replacement but the "mA" is "300mA"
and
I was worried that this might cause some damage. Hope that clears up any
misunderstandings.

Perhaps it has a typo?
Not on my part, although I did wonder whether the "20mA" should actually
read "200mA". You can see a picture of the adapter with specs he
http://www.vicsplace.pwp.blueyonder.co.uk
Would be interested in your reply after you've seen it.
Your help is appreciated.
Vic



Well that does certainly say 12V DC 20mA, though I suspect it might be a
typo on the adapter. I say go for it and try the 300mA adapter, it should
work just fine.