Charging with a 10w charger won't hurt your phone. Because the mobile phone itself supports 10w power fast charge, so it is just good for him to use 10w fast charge, even if he does not support 10w fast charge, it will not be broken, because he will charge at low power, to a certain extent, protect the battery, when a smart phone is connected to the fast charger, the charger and the phone will handshake agreement, To ensure that the standard supported by the phone is exactly the same as the standard provided by the charger
This has little impact, so if you charge with this power, the loss of the battery is relatively small, which is a benefit.