An offline power supply includes a power supply circuit including a primary-side circuit for connecting to a first power source, a secondary-side circuit for connecting to a load, and a transformer connecting the primary-side circuit and the secondary-side circuit. A switch operates to selectively connect the primary-side circuit to the first power source. A second power source is charged during operation of the power supply circuit. A controller powered by the second power source has at least one input, and an output to selectively operate the switch based on the at least one input.