Which of the following is characteristic of a switchmode power supply as compared to a linear power supply?
Why A switchmode supply chops the DC into a high-frequency square wave, typically 20 kHz to several hundred kHz, before transforming and rectifying it. Transformer core size and filter capacitor/inductor values needed for a given power level shrink as frequency rises, because each cycle moves less energy and the core has less time to saturate. That is why a switcher delivering the same current as a 60 Hz linear supply can be a fraction of the size and weight.
Watch out The claim about fewer components is backwards: switchers need an oscillator, switching transistor, feedback/regulation circuitry and RFI filtering, so they usually have more parts than a simple transformer-rectifier-regulator linear supply. They are also noisier electrically, not inherently more stable.
Higher frequency equals smaller iron. Switchers trade 60 Hz bulk for kHz switching, plus some RF hash.
A phone charger fits in your palm because it switches at kHz: higher frequency, smaller parts. The 60 Hz linear supply is the brick.