A two-stage AC-DC power converter for powering a load at a substantially constant current, and related methods and systems. The first stage of the AC-DC power converter includes a conventional power factor correction (PFC) circuit that outputs a direct current (DC) voltage and a DC current. The second stage of the AC-DC power converter includes a low voltage flyback circuit that receives the DC voltage and the DC current. The low voltage flyback circuit includes a flyback transformer and a switch circuit that selectably toggles the substantially constant output current provided by the low voltage flyback circuit to the load between a first and a second, preset constant current. The secondary windings of the flyback transformer are split into two sections, and the switch circuit toggles the two sections of the secondary windings between a series and a parallel configuration to provide the first and second, preset constant currents.