A genesis 1 power supply won't work anyways, the tip is tool small on it's inner diameter. Just so you know, a 12volt 1.5 amp power supply will work just fine. Don't worry about matching it perfectly, that extra volt won't hurt anything, a voltage regulator in the system makes sure of that. You can get a suitable power supply from ratshack, but they charge a ridicilously high price, something like $30. Besides that, the first one I got from them was defective.
If you are handy with a soldering iron, you can grab a genesis 1 adapter and change out the cord. An atari 5200 power supply would work perfectly if it weren't for the polarity. Other than that, as far as game consoles, you are going to need an original, or go to a junk shop and see if you can't find a suitable old power supply. If you can't get one in the next month or so, I can probably grab one for cheap the next time I am at my local junk shop. Or I could mod a genesis 1 adapter for you.