The fan on my power supply was very loud, so I removed it, and the cover of the power supply also. I designed a new cover for it, with an opening for a 120mm fan that I had extra. I connected the fan to the 12V output of the power supply, so now it is constant speed, but still much more quiet than before, and also better air flow.
I mounted the fan to blow the air out, same as the original fan.
You will need:
10 x M3 nuts
10 x M3 8mm long screws
NOTE: The part is 197.5 mm long
I designed it so that it does not need supports.