As we have mentioned in other articles and reviews, the first place we look when opening a power supply for 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, yellow component on the pictures below) and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components, usually removing the MOV and the first coil.

This power supply is flawless on this stage, having two more ferrite coils (one of them is behind the printed circuit board in Figure 6), four more Y capacitors (two of them can’t be seen in Figure 6) and two more X capacitors than necessary.

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Figure 6: Transient filtering stage (part 1).

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Figure 7: Transient filtering stage (part 2).

In the next page we will have a more detailed discussion of the components used in the ST-550P-AG.