As we mentioned on other articles and reviews, the first place we like to take a look when opening a power supply to have a hint about its quality is its filtering stage. The recommend 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 than that, usually removing the MOV, which is essential for cutting spikes coming from the power grid, and the first coil.

On this section this power supply is flawless, as it has more components than the necessary – one extra X capacitors, one extra coil and a ferrite bead on the main AC cable. It also provides one X capacitor and two Y capacitors after the rectifying bridge.

click to enlarge
Figure 6: Transient filtering stage (part 1).

click to enlarge
Figure 7: Transient filtering stage (part 2).

Now let’s have a more detailed discussion on the components used on EarthWatts 500 W.