Nobody available to hear me...?
It is a major holiday in many parts of the world today.
The BEST charger is always the one that is packaged with your phone, or a direct replacement in terms of output.
The chip in your battery will regulate the amount of charge coming into the battery, but constantly throwing more charge at it than needed is never good.
I'm sure in the short term an AC-60 might be fine and would charge your 640 XL, but at what cost to longevity of the battery in overall charge cycles it can handle?