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Yes,if you use an adapter with larger output in mA,it should charge faster. If not,the opposite occurs.
I don't have M or SP, but you need to think that SP will charge in a longer period of time as it has a larger battery.
EP800 has 850mA output,which means M will need about 2 hours,a litlte over maybe. And SP a maximum of 3 hours.
Can you boot both devices in safe mode and see if anything changes?
/t5/FAQ/How-to-boot-your-phone-into-safe-mode/m-p/348008#U348008