ColorSageTrue. Service center has nothing to do with this issue.
I don't think the servicing will help. Not every 9V charger is Qualcomm QuickCharge 4 compatible. If it's not it will revert to 5W as it is a USB standardized max power draw. The charging speed is negotiated via phone-charger handshake.
shiv1gThis is most probably not a bug. Rather a question about if there was a proper handshake between the charger and phone. What I'm saying in plain English is that they are not compatible. This is why your phone defaults to only 5W. It's a security thing. If the charger is a cheap Chinese charger that doesn't support the right charging protocol, this is what happens to prevent any accident from happening.
True. Service center has nothing to do with this issue.
I have tried to replicate the charging issue on my friend's 6Z with 3 regular 10W chargers, and surprisingly got the same results. Both the phones would only charge at just 5W.
It's easy to understand that it has basically nothing to do with the device hardware and neither with the chargers. As many other smartphones Oneplus 3, Xiaomi, Samsung and realme when plugged with the same 10W chargers, would easily draw the full current and charge at 10W speed. However, for some unknown reasons, 6Z just doesn't like to do the same. Why is that?