A power supply can regulate the power from a wide-input power source. The power supply can provide regulated voltage and current and can work in either a constant-current mode or a constant-voltage mode. The power supply includes a switchable charging path and a switchable discharging path, each coupled to the output in series with a current sensor and in parallel with a voltage sensor, wherein the current sensor and voltage sensor provide signals to a control circuit for controlling the switchable charging path and the switchable discharging path. The power supply can rapidly and dynamically switch between a charging state, a freewheeling state, and a discharging state.