Transient Filtering Stage
As we have mentioned in other articles and reviews, the first place we like to look when opening a power supply to have a hint about its quality is its filtering stage. The recommended components for this stage are two ferrite coils, two ceramic capacitors (Y capacitors, usually blue), one metalized polyester capacitor (X capacitor), and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.
In this power supply, this stage is flawless. It has one X capacitor, three Y capacitors, one ferrite coil, and one MOV more than the minimum required. Besides having two MOVs squeezed between the two capacitors of the voltage doubler circuit, it has one at the power supply input – all three MOVs can’t be seen on the pictures below.