I bought a Yobo replacement power brick to check it out. Not Trusting yobo, I hooked up the power brick to my voltmeter. Rated for 9v @ 850ma, it returned 17v @ 1800ma ! Concerned and a bit shocked, I checked the stock SNES adapter rated at 10V @ 850ma and it returned 13V @ 5A Gensis/MD 9V @1.2A returned 13V @ 5.5A TG-16 10.5V @ 730MA returned 13V @ 5A And for comparison, a radioshack variable. 9V @ 330ma returned 9.5V @ 3.3A 6V @ 330ma returned 3.5V @ 3.3A I know all these devices have some level of power regulation, but throwing 17V into a 9V device can't be good.
You have to test devices under a load, measure the voltage across a LED (with series resistor), it will be closer to the rated amount certainly. Also dunno where you're getting the current ratings but I really doubt those are accurate, besides, a 5.5A supply is a very very good thing! Wall warts typically aren't regulated, most are just a transformer, a full bridge rectifier and a big smoothing cap. This in my view is a good thing since regulation happens inside the console (wasteful to regulate the voltage twice), and it keeps costs and failure down and current up. It's true though, for most consoles you want as close to 9V as possible, since with a linear regulator in old consoles excess voltage is burned up, and for high current consoles that's a lot of heat. If one of those adapters really does put out 17V under a load, I would certainly not use it, there's something already wrong with it.
That was my first thought, I remember hearing those adapters output a much higher reading if it's not under load.
Most, if not all cheap wall-warts will put out 15-18v under no load. Put a load on them and the voltage drops down much closer to what they're rated. Basically, if the console has a regulator inside it (almost all do) there's no difference.
I was thinking the same thing marshallh, but given how consoles age, this could become more of a problem.
The 7805 regulator that you find in the Genesis/Megadrive (and a ton of other consoles) is pretty bulletproof. When it does fail after a million hours of continuous operation, it just ceases to output power at all. But that hardly ever happens, and the 7805 can safely convert up to 40 volts as long as it's sitting on enough heat sink. I totally understand why you would be worried about the voltage. I once shorted out a trace in a laptop, and it caught fire when I plugged it in.
and still wondering of how you got your current rating you mentioning in your post above, assembler? if a transformer puts out several amperes, and even more than it is basicaly rated for, then the output voltage should sink far below the rated voltage of e.g. 9V.
Actually, for up to 18V output the 7805 takes a maximum of 35V. 40V is only for 24V output ;-) Still, it should be happy regulating 17V down to 9V. As for current, well firstly it doesn't matter as long as it is OVER the required current. Your device will just take what it needs. I would also question those values, though. Don't forget, you have to connect an ammeter in series with a suitable load (i.e. the console) to get an accurate reading.
