A power supply comprises a rectifier, a transformer, a switching member, a controller and a voltage blocking clamp. A power supply can receive an alternating current (AC) input voltage having any magnitude within a wide range of AC input voltage magnitudes and can produce from any such AC input voltage magnitude a direct current (DC) output voltage. The voltage blocking clamp comprises at least one transistor connected between the rectifier and the transformer and switching member that limits the amount of rectified AC input voltage applied to the transformer and switching member to a predetermined amount when the rectified input voltage exceeds that predetermined amount. When the rectified input voltage exceeds the predetermined amount, the amount of the rectified input voltage above the predetermined amount is applied to the at least one transistor instead of the transformer and switching member.