I have a master system and a baseball but that is it, and contrary to popular belief it won't work with a sega genesis powerpack and I don't care to pay some of the outrageous prices I saw on ebay and risk those not being the right specs either I guess I could try radioshack I remember reading someone found a universal one for sale that worked.
There must be some confusion which versions you're talking about.
Model 1 Master System has a 9V DC, 1A, negative barrel tip.
Model 1 Genesis has a 9V DC, 1.2A, negative barrel tip.
The model 1 Genesis brick will power the model 1 SMS just fine. Higher amps from the power pack is ok. As further proof of this, the bottom of the SMS calls for 850 mA (.85A) and says to use plug pack model 3025. The 3025 brick puts out 1A as noted above. Voltage and polarity need to be the same, as well as the plug tip obviously.
I have no idea what the model 2 Master System plug looks like as I do not have one.
Model 2 Genesis uses a 10V DC, .85A, positive smaller yellow tip.
So maybe you were looking at a Gen 2 brick or a SMS 2 system?