A switching mode charger capable of performing mode switching to adjust and output charging current for a battery or driving current for an external circuit element includes an input terminal, an output terminal, a Buck-Boost converter, and a controller. The Buck-Boost converter generates a voltage at the input terminal according to a voltage at the output terminal or generates a voltage at the output terminal according to a voltage at the input terminal. The controller dynamically selects an operation mode from a plurality of operation modes as an operation mode of the Buck-Boost converter according to at least one of the voltage change and the current change that are associated with the Buck-Boost converter, wherein the Buck-Boost converter dynamically performs mode switching according to the operation mode selected by the controller so as to adjust and output the charging current or the driving current.