The fan works so far, but not the fan controller. Any advice is much appreciated. Seems like black is negative, and yellow positive. Not sure what to do with the red wire.
I believe red is hot (positive, power), black is neutral (negative), and the yellow wire is a ground that should be left out and taped off unless your plug has a ground, which most don't. So, you'd run black from the plug straight to the fan and the red from the plug to the controller to the fan.
yellow is the remote wire for digital controllers. the controller needs to be tapped into the red wire. The manual controllers just adjust the amount of power going through the red wire. I'm pretty sure that's how it goes..I've wired up quite a few of these but I'm pretty stoned right now.
Exactly what he said ^^^ Yellow is the ''rpm sensor'' for the computer to read the fan speed so it can adjust properly, for an application like yours, the yellow wire is useless. If the speed controller doesn't work you can find different voltage power source, from any AC to DC Appliance. (ie Cell phone charger and most Appliance power supplies, I used my old laptop's power supply, but it ran at 18 volts instead of 12 so the fan were running a bit too fast lol.) So basically, Voltage will be decide the fan's RPM. If you are able to source an old Dimmer switch from a DC Appliance (like a rheostat from a car's interior light) You would probably have a ''plug and play'' speed controller right there.
Ok guys, I've done a little more tinkering and the fan spins when I connect the cables from the DC adapter to the black and the yellow wires, but I'm still unsure of what to do with the red wire which is probably why the controller isn't working
Yellow does not apply in this situation. Its for a digital controller, which you don't have, or a computer running temperature control software. As the others have explained, you can adjust the speed by adjusting the voltage. That's what your controller is doing. Dialling the voltage up or down. So it needs to interrupt the hot (red) wire between the plug and the fan.
Red wire: Plug --> controller --> fan The red wire from the fan goes to the controller. Your hot wire from your plug goes to the controller. In your picture, where the red wire from the controller splits into a Y, one end goes to the hot wire from the plug, other end goes to red fan wire. Whatever wire from the plug you were wiring to the yellow, wire that to the red from the controller and forget the yellow wire ever existed.