Every year, millions of Watts of power are lost in heat from inefficient linear AC/DC wall adapters. This loss is incurred even when there is no load applied. The cause of this inefficiency is energy lost from leakage elements found in the transformer and electrolytic capacitors. This reference design shows that by using a switch-mode power supply (SMPS) instead of a linear supply, the amount of wasted energy can be drastically reduced. Additional circuitry, “wakes up” the power supply only when a load is applied, reducing losses to just tens of milliwatts.