Be very careful if you go inside the PSU to replace a fan. There's a lot of voltage hanging around for a long time after switch off.
The fan is normally a standard type - but the power leads may be soldered to the board, or have an unusual plug . If they're soldered to the board, do not take the board out and unsolder them. Cut the wires, and make a tidy join - make sure you connect them up correctly, or the fan will go backwards.
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