From Hack a Day:
[Mike] just purchased this Atten APS3005S bench power supply for around $80. It does the job, but boy is it noisy! We were pretty surprised to hear it fire up in the video after the break. To make matters worse, the noise is persistent since the fan never shuts off.
Having worked with other bench supplies he knew that a common feature included in many models is temperature controlled case fans. He set out to quiet the fan and implement a temperature switch.