This is because the output of the mobile power supply does not match the input of the phone. When charging the mobile phone, the mobile power supply must first sense the current of the mobile phone before charging normally, when the output current of the mobile power supply is relatively small, the mobile phone may automatically disconnect and charge in order to protect the battery, this time the mobile power supply can not sense the current of the mobile phone, the mobile power will misjudge the mobile phone has been full, and it will automatically disconnect and charge.