If you have a 9v or 6v DC output that will work too, the fan will just run a little slower. Try to find one that is 500mA or more and no less than 6vDC. 6v is okay for a very small incubator like one of the foam tabletop incubators.
If you have a voltmeter, you can figure out which is + and which is - ahead of time, otherwise just twist the wires and hook them to the fan one way, see how much air is blowing, switch and try the other way. If the fan has a red, yellow and black, just use the red and black. The yellow is a speed sensor.
It's a good thing the fan burned up before you started a fire.