I've never owned a working Sega Genesis. I've played on one quite a few times back in the day with Fallguy40 and have known some other guys who have owned one in the past, but personally I've never owned one. They are obviously easily obtained and pretty cheaply, but I have been determined to wait until I find an outstandingly good deal before I get one.
A couple of years ago while I was in Rhode Island I noticed a person on Craigslist that was selling their complete Genesis model 2 with the box, Sonic Spinball, controllers, instruction manual, etc. for $5. So I figured OK let's go grab it and I'll shove it in my suitcase. So we drove out there and did just that. When I got home to Texas I plugged it in and guess what - it didn't work. So now I own a $5 copy of Sonic the Hedgehog Spinball with no system to try it on - fair enough.
Two years and hundreds (or if I include eBay thousands) of potential Sega Genesis purchases later I see on Craigslist that a guy in my very town not even 3 miles down the road is selling his Genesis Model 1 with a controller but no AC adapter cord for $6. I figure - OK cool, I'll just use my useless power cable that I got with the Genesis 2 and I'm goood to go. But Sega would have none of it. Turns out that even though the 3 different models of the Genesis were fully compatible with each other game-wise, for some reason Sega decided to make their power cable for the model 1 with a negative tip polarity, but for the following 2 models they went with a positive tip (the more conventional apparently). The nice fellow I bought it from did actually inform me of this and said I would most likely fry it if I tried to use the model 2 cord - which fits perfectly. Now why the hell would Sega do that?? So anyway, I thought I might be able to use a universal power supply I have so I bought it. I got it home and my universal power supply could match the voltage but didn't have near enough amps.
So now I own 2 Sega Genesis systems (Genesi?) and still no way to play this damn copy of Sonic Spinball that I probably won't like anyway.

