An embodiment of a power supply includes an input node operable to receive an input voltage, an output node operable to provide a regulated output voltage, an odd number of magnetically coupled phase paths each coupled between the input and output nodes, and a first magnetically uncoupled phase path coupled between the input and output nodes. Such a power supply may improve its efficiency by activating different combinations of the coupled and uncoupled phase paths depending on the load conditions. For example, the power supply may activate only an uncoupled phase path during light-load conditions, may activate only coupled phase paths during moderate-load conditions, and may activate both coupled and uncoupled phase paths during heavy-load conditions and during a step-up load transient.