Upon further examination of the fan in this supply, it appears it is a non-standard 4-wire fan. The additional 2 wires are hooked up to two thermistors in parallel, one on each side of the heatsink. The fan speed control apparently is happening inside the fan itself, so replacing this fan won't work unless I want one that is constantly running at full speed.
It's an odd design. The fan power comes from the front panel as a 4 wire connector that ls the same JST XH as the fan itself, but those 4 wires are +14, +14, GND, GND, which is then regulated to 12 on the rear board for the fan.
Anyway, now I'm trying to see if I can source a replacement fan from Siglent or D-Fan (the manufacturer of the fan) since I think it's a customized part.