When it comes to the Sega Genesis power supply, there’s one important thing to remember. You can use a Genesis power supply in a NIntendo NES, but the reverse is not true. The NES isn’t picky about its power, but the Genesis needs 9 volts DC and the right polarity.
The original Genesis power supply connector is the same size as a Nintendo NES, but the Genesis requires 9 volts DC, center negative, and 1 amp, though 1.2 amps is better. A non-Sega adapter is fine to use as long as it meets these specs, but using AC or the wrong polarity will damage the game console.
Sega Genesis power supply specs
The early model Genesis uses a 2.1mm barrel connector, just like the NES, and it’s probably the most common plug size you’ll find. The odd thing about the Genesis is that it uses the center as negative. It’s much more common to use the center as positive.
So if you’re scavenging around for a substitute AC adapter, make sure you find a center-negative plug. Or just buy a replacement Genesis AC adapter that advertises itself as being compatible with your unit.
Most game store sell power supplies that will work with both the Genesis and the NES. This is because the NES doesn’t care about AC or DC or polarity. These dual-use supplies are safe to use. A Nintendo-branded AC adapter, or an AC adapter that matches Nintendo’s original specs, is not.
Deviating from the original Sega specs
You can safely deviate slightly from the original Sega specs, as long as you get the polarity correct. A Genesis will tolerate a bit more than 9 volts, so it’s OK to go to 10 volts, or even 12 volts. Just keep in mind more voltage means more heat to dissipate, so the Genesis will run hotter, and over time this can decrease the console’s life expectancy. So even though 12 volts will work, I recommend against it.
Amperage is the other concern. Sega originally specified 1.2 amps. A Genesis will run on 1 amp, but it’s better to give yourself some headway on amperage to avoid burning out the AC adapter. You can go high on amperage without damaging anything, as the unit will only draw the amperage it needs. Having 1.2 or 1.5 amps available is fine; the unit will draw what it needs, and the power supply will run cooler since it’s more than strong enough to meet the console’s needs.
Sometimes an AC adapter will measure its current rating in milliamps, or mA, instead of amps. Just remember 1000 mA is one amp. So you want 1,000-1,200 mA to power a Genesis.
Genesis 2 and 3 power supplies
The Sega Genesis 2 and 3 power supplies are physically and electrically different from the original. They are not interchangeable with one another. The plugs won’t fit, but if you force it and try to use it anyway, you’ll damage the console.
The AC adapters for the Model 2 and Model 3 supplied 10 volts at 850 milliamps and have a slightly smaller 1.7mm plug, also known as a EIAJ-03 barrel. They do have the more common center positive polarity.
These supplies are physically and electrically incompatible, so if you have a newer Sega Genesis model 2 or model 3, don’t buy a power supply intended for the original Genesis. Get one for the Model 2, so you get the correct polarity and the correct plug size. The Sega CD and 32X add-ons used the same connector and polarity as the Genesis model 2 and 3 used, so those AC adapters are completely interchangeable with one another.
As is the case with the original Genesis, you can go high on amperage without hurting anything. It’s not uncommon for newer revisions of game consoles to have a reduced parts count due to improved technology, and the newer technology tends to make the systems more power efficient.