Which Sega PSU is the 9V one?

[Super Monkey Balls]

I think the MD1 power pack is 10V. Is it the MD2 PSU that's 9V?

[MD]

The MD have various PSUs, none of them make a blind bit of difference in running a MD or any other console, including the Neo Geo (which is what I assume you want it for...).

The voltage is regulated inside the machine so the extra 1V makes no difference.

[Super Monkey Balls]

Groovy. I have a 10V one I used for a Pro Pow 3 console but I thought I'd need a 9V one for a Pro Pow E. Saves me some hassle.
Cheers MD