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, yellow component on the pictures below) and one MOV (Metal-Oxide Varistor). Very low-end power supplies use fewer components than that, 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 on Figure 6), four more Y capacitors (two of them can’t be seen on 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).

Now let’s have a more detailed discussion on the components used on ST-550P-AG.