A three-level buck converter circuit configurable to transition between a three-level buck converter mode and a two-level buck converter mode and methods for regulating power using such a circuit. One example power supply circuit generally includes a three-level buck converter circuit and a control circuit coupled to the three-level buck converter circuit and configured to control operation of the three-level buck converter circuit between a three-level buck converter mode and a two-level buck converter mode. The three-level buck converter circuit generally includes a first switch, a second switch coupled to the first switch via a first node, a third switch coupled to the second switch via a second node, a fourth switch coupled to the third switch via a third node, a first capacitive element coupled between the first node and the third node, and an inductive element coupled between the second node and an output node.