Stir plate question

Have the pieces now to assemble. The cooling fans I have are three wire and the power supply(cell phone charge) is two wire. What is the correctr wiring for this.

Your cooling fan has a third wire for a temperature sensor. My guess is a yellow wire. If it's not yellow, you can look at the fan and find the temperature sensor and the color wire that's soldered to it.

You can ignore it and wire up the other two wires.

black and red are gnd and power, respectively.

The extra (white?) wire is usually a tach wire. It is not useful for your purpose (it carries a signal that pulses at a frequency relative to fan speed). Leave it unconnected and, when everything is working perfectly, cut it.

Some fans (from Dells) have a built-in thermistor, seen near the fan blades. These will be a problem to use. They regulate the fan speed based on detected temperature. The thermistor needs to be shorted to get full speed. The ones like this that I have seen did have a third wire.