I use oryginal charger 12v 1,5a that come with phone, it charge 9v 1,67a so i think it support pump express but cant switch to 12v on some reason.
Charging start from 5v, next switch to 7v, after few seconds switch to 9v and stuck on it.
Factory reset is big problem to configure again all phone. I can make this only i have 100% that solve problem or is spossible to make any full backup that can restore if dont work to back all previous settings.
Just backup your stuff and check for the Google account automatic backup function.
Unfortunately a factory reset is always the first step to rule out issues.
I also recommend to try another charger which supports the mediatek pump express protocol. I need to know if your original charger is faulty or not.