a switched-mode power supply can be made more compact, as well as lighter in weight, by designing it to operate at much higher frequencies than mains power.

wikipedia has an article on such power supplies:

https://en.wikipedia.org/wiki/Switched-mode_power_supply

there are other web pages describing them as well, such as:

https://www.electronics-tutorials.ws/power/switch-mode-power-supply.html

these can describe things better than i could. i have not been working in power supply design for a long time, so quite rusty.

2/fin