The Samlex SEC1223 power supply has an internal fan that should turn on when the supply gets hot. But the thermostat must be set rather high, the supply gets warm bur not hot without it ever activating. So I figured I'd make the fan be dual powered. Normally the fan is controlled by a transistor, Q5, a 2N2222. The fan positive lead goes to the 13.8V output, and the negative lead goes to this transistor's collector. If the thermostat goes open, the transistor turns on, turning the fan on. I added a 68Ω power resistor from ground to this transistor's collector, to run the fan at a low power level, and low audio noise, when the supply isn't so hot that it triggers the thermostat. This will keep the supply cooler, and should help make the caps last longer.

Hi Wa2ise,
Good idea using the TO package resistor.

I used the same tactic on a Studio Bass amp where the fans were far too noisy for quiet use but used PW5 package resistors across the thermostat
Most of the time the fans just idle away and keep the heat sinks at warm, if the volume gets cranked up then the full fan noise does not matter!

The TO package could bolt onto a heatsink or chassis nicely.
Have not seen them for sale.

Fred.

I have some low noise Arctic brand fans that I bought to replace the noisy fans in my Tenma power supply which operate full blast regardless of load. They come complete with a temperature sensor that varies the fan speed with load demand.

I have a bench power supply that runs its fan at a few different speeds depending on the load.

Ditto ... I think mine was a thermostat driving a Pulse Width Modulator chip, driving the Base of a transistor.
Wa2ise solution is an elegantly simple alternative.