More specifically, to meet noise suppression requirements it is generally required to have an X capacitor across the AC mains to keep differentail noise local to the system. This is indicated as C1 on the schematic shown here. In addition, Y capacitors are generally placed from a side of the AC mains to the system‘s chassis ground for the suppression of common mode noise. This is indicated as C2 and C3 on the schematic. Please refer to the VY1 and VY2 datasheet to see which capacitors will meet the a design‘s particular requirements.