Thanks John,
That's the answer i was after, and is how i have it hooked up at the moment.
I have a slot.it controller module for scalexetric home set turning up today and didn't want to fry it with my variable power supply being wired wrong to the sport power base.
I am waiting for the sport power base to fry though, but it seems to be running just fine at 10v to the rails. I guess time will tell.