I have a 'bench' power supply, a BK-305D from the well-known brand 'baku'. It works, it was cheap. Its loud. Or, should I say, it *was* loud. And that is today's hack. Silence the supply.
If you open this up, its a pretty typical linear supply. A big transformer, a small amount of low-tech electronics. And a 24V 80mm, hard-wired to a 25V rail. Here we can see it in its naked lid-removed glory.
Note: the capacitor holds some power on the 25V rail, so after you remove the lid, consider shorting it or waiting a while.
OK, seems straightforward. We'll go get a 80mm 4-pin PC case fan (about $10 from Canada Computers), and then a buck-boost converter to conver the 25V to 12V (about $1), and a fan-controller.
The fan controller I choise is a ZF1X4-1707. it was $2 from Aliexpress. But there are lots of them around, they all kind of do the same thing. It came with these cryptic instructions, below, on how to use the 1-button and 3-led's.
The buck converter module I chose came in a 10-pack for $2, and was adjustable. I adjusted its output to be about 14V.
After this, it was a simple matter. I glued the temperature probe to the heat sink, swapped in the new fan (blowing into the case), clipped the power lead from the old fan and put it into the buck converter, from there to the fan controller, from there to the fan.
If we have a look with the FLIR, we can see the TO-3 are about 45C when shorted at full power.
The fan is normally silent, and, when running full speed, is still an acceptable volume.
Great success! Cost about $15 ($10 for the fan, $2 for the controller, $1 for the buck converter).