On this fan, I first attached the "dongle" that adapts the 3-pin connector on the fan to the 4-pin old-school molex connector. This is to help figure out which conductors are positive, negative, and speed sensor, because the new fans did not have color-coded conductors. (The speed sensor will not get used here)

Mark on you new fan which conductor is black (negative), and which is positive (red).

Once you have marked the cable, cut the 3-pin connector off.