Cheers for the replies,
Will look through my random collection of old PSUs over the weekend to see if I can find a 5v 1-2A supply, but I think I'm lacking one that fits that description. Bit more info, no the LED doesn't come on, and I now believe the PSU might be working (it gets warmer) thus it might be the machine - it was sitting in a loft for 25 years after all! Will take it apart and clean connections first to see if it makes a difference. Will be good to find an adapter that works as is, as I really don't want to butcher a decent supply for something else.
I've got it hooked up via RF but as I'm getting no LED, and no power running through it, there's nothing happening (no pops or whistles or any signs of life unfortunately). I've a voltmeter but as you can probably tell, I'm kinda new to this.
Edit: OP won't disappear even if you go offtopic. I'm happy soldering, and have added language and Hz switches to my Megadrive but that's about the limit of my PCB manipulation so far.