Electrical Issue, please help!

I'm building a Son of Fermentation Chiller, and I bought a 12v dc 250 miliamp fan, and a transformer that outputs 12v dc 300 mA. The fan has three wires (black, white, and yellow. I assumed that the black one was a ground.

I hooked it up to the power supply and a small amount of smoke came out and it did not spin. Very Bad! So I tested it with a nine volt battery and and it didn't go at first, but I blew on it a little and it began to spin.

Could the 50 mA difference in my power supply and fan have ruined my fan? What should I do?

Likely:
Black isn't ground, its negative. White is positive. Yellow would be unused for this (probably an RPM sensor).

But, consult your fan documentation. 50mA probably didn't fry the fan, but I would guess your RPM sensor is hosed now.

Thanks for the quick reply. Actually, I forgot to mention that when it smoked, I hooked up the black and white wires. But when I got it to go with the 9V battery I used the yellow and white wires. So maybe the color-coding is messed up and the black was the rpm sensor. That still wouldn't explain why, when I hooked up the yellow and white wires to the power supply, the fan didn't spin. Sorry I forgot to mention those specifics earlier. Does that extra info help?

Just as a FYI aside, milliamp ratings on devices that use power are how much current the device will draw. The same ratings on devices that supply power are how much current they are capable of safely delivering. Current draw is actually a "result" and not a potential like voltage. IOW, your 300mA supply doesn't shove all the current into the device. The fan would just take the 250mA that it requires. You could have supplied that fan with a power supply rated at 10,000 mA and it wouldn't be the cause of the smoke as long as the voltages matches.

Well computer fans use Black for Ground (0VDC) I hate saying negative because it isn't a negative voltage to ground....

The computer fans use Red or Yellow for +12VDC and Yellow, White or Green for the fan speed sensor.

So I would suspect that you would use Black and Yellow.....good luck

Given what you all have said, I probably toasted the rpm sensor. That's very helpful to know, Bobby. So I probably didn't fry the +/- terminals. I guess I'll keep messing with it until I find something that works.

Update: when I connect the white wire to the negative terminal on a 9V battery and the yellow wire to the positive terminal, the fan spins. But when I do this using the power adapter nothing happens. Any idea why?

I would suspect either you have the polarity reversed or you damaged your power supply.

Did you try Black and Yellow and if so what happened?

I tried the black and yellow and there was a tiny bit more smoke, but no fan spinning. I've tried all combinations and only the black wire makes it smoke, so that must be the rpm sensor. I think the power supply is somehow broken. I'll get a new one and see if that alleviates the problem. Thanks!

try hooking your black to black, then your other two to your positive wire (yes both) Thats how I got mine to work.

I tried my adapter with a friend's fan and it worked fine. It looks like I'll just have to get a new fan.