Looking at AC Adapters for SMS/Genesis model 1... originals were 1 and 1.2 amp, but some of these new ones are as low as 350 mA... how much does it matter? Will low amperage ones just burn out faster (from what I've read online)?
Then you have carts like Virtua Racing and Everdrives which take even more power. I wouldn't chance it. I'd stick with the original amperage ratings or better.