Switching Mode Power Supplies are using a clock signal instead of an analog regulator. This way the transistors won’t be heavily under load all the time and power dissipation is much lower.
There are a lot of types of SMPSs, e.g. primary and secondary clocked, buck and boost converters, flyback converters, half- and full-bridge push-pull-converters, forward and backward converters etc.
But in theory they all work on the same idea that voltage and current each are temporarily stored. For this each converter has at least one capacitor and one inductor. Via PWM the output voltage can be regulated as well as the current. Since the topic about SMPSs is really complex I will not explain everything here, but there are a lot of fully integrated ICs for this. As example I’ll mention the LT1074CT7 (with programmable current limiting) and the MC34063 (also used in Nixie clocks). These are common and simple integrated regulators.
If you want to design SMPSs, I’ll advise you visiting the website of Schmidt-Walter, there are a lot of different types explained and you can calculate the specs for them.