Two major categories of AC-to-DC power supplies are linear and switching power supplies.
Linear power supplies employ a large transformer to convert the AC voltage down to a lower amplitude, followed by a series of rectifier and filtering circuits that produce a very clean, ripple-free DC voltage. Linear power supplies typically have the disadvantage of being much larger and heavier than equivalent switching power supplies.
In contrast, switching power supplies use a switching regulator to control high-power pass transistors that feed fully rectified and filtered AC line voltage into a step-down transformer and additional rectifying and filtering circuits.
While more complex in design, switching power supplies are more efficient, smaller, and lighter than equivalent linear power supplies. Modern switching power supplies can provide low-noise DC output equivalent to that of linear power supplies.