Me too. Like maybe we could convert to DC at the breaker box so I didn't have to be haunted by the squealing capacitors in all of the power supplies that are scattered around my house.
It's the coils that squeal, they're the only part that has anything that can move mechanically.
In the olden days of the late 80s when I had a high school job at weekends repairing TVs there was a particular family of Bang and Olufsen TVs where you had to desolder a choke in the power supply, smear it all full of some sort of resinous goo (they recommended a particular epoxy; I found that Isopon car body filler was the gold standard, setting into slightly flexible polyester that didn't fall off or crack).
Within the repair industry it had been nicknamed "Beobuzz", after all the other "Beo<something>" products.
Huh, I figured there had to be AC in there somewhere because otherwise where is the frequency coming from? Or is there a conversion to AC somewhere in the middle of a DC-DC conversion? I had assumed you could achieve it with just resistors. I am ignorant about the physical nature of electronics.
What happens is that the AC is rectified to DC and then it is chopped up at many kHz (10-100). The idea being that the higher the frequency, the smaller the inductors, capacitors and transformers can be.
Even if the switching frequency is ultrasonic, it can still excite audible mechanical effects in windings of transformers and other elements to create the canonical coil whine. This effect depends on certain ranges of duty cycle (system load) creating periodic spikes in power.
