According to one aspect, a DC power supply is provided. The power supply includes a first input configured to be coupled to an AC power source, a second input configured to be coupled to a battery, an output, a transformer, and a controller coupled to the transformer. The transformer includes a first winding configured to be coupled to the first input, a second winding configured to be coupled to the second input, and a third winding configured to be coupled to the output. The controller controls, in a first mode, the first winding to generate, based on power received from the AC power source, a first voltage across the second winding to charge the battery, and a second voltage across the third winding, and control, in a second mode, the second winding to generate, based on power received from the battery, a third voltage across the third winding.