Due to the design of EMI, there will be some Y capacitors between line and neutral to the FG (case) to improve EMC. These Y capacitors will cause some leakage current from line or neutral to the case (normally case will be connected to earth ground). IEC60950 also has a clear specification for this phenomenon, information about leakage current of the device must be less than 3.5mA, it should not cause harm to the human body.