It's MTK pump express charging technology. It's safe and I controlled. The phone chargers with 5v 2A once plugged in, then the IC will communicate with the charger, if it equipped with fast charging and responds to the message, the phone will switch to 9v 2A and then 12v 2A and all these things can happen less than 5-15 seconds.
The latest pump express if the 12v 2A is correct is even better than Qualcomm quick charge 3 with 12V 1.5A but yeah the general believe is that what ever Qualcomm does is better than MTK which is just a myth.
All quick charge drops back to normal charging when the battery