

Why do some AC adapters and power supplies make this whining noise? Why do some not make this noise? Is there anything that I can do to suppress it? This happens most often when they are not connected to a device or otherwise in use, and stop making noise when I connect a device that is not fully charged. However, I often hear a whining noise from some of these power supplies. I have many different AC adapters and power supplies for a variety of devices, ranging from small 5V/1A USB chargers to laptop power adapters and desktop PSUs.

SuperUser reader Rishat Muhametshin wants to know why some of his AC adapters and power supplies make a whining noise:
