Your charger is flash charge. Does your phone support flash charge?
If your mobile phone does not support flash charging, it can not achieve this effect of flash charging, there is another possibility that your mobile phone does not have real static electricity, which will lead to less and less charge for a while to find your mobile phone power consumption is larger than the amount of charge, so it will be more and less charged, it is recommended that you carry out the corresponding check, there may be a problem with the charging port charging line or mobile phone battery
Maybe the battery is old, or turn it off and charge it
Maybe the charger is broken. It won't charge