There are many schematics and many controller chips out there. Just search for "SMPS".
The most important part is that the frequency can be stepped up from the original 60Hz (or DC) to a high frequency which means a far smaller, lighter, cheaper transformer can be used since it makes much more effective use of magnetic materials as well as the capacitors. It won't hum in the audible range. The output ripple and EM leakage is also outside the audible range so you won't hear any of the power supply in an audio output.