Can different power socket in one house charge at different speeds
Highly unlikely that the charging points are centralized. Much more likely that each USB charging point is its own device, each with its own connection to the mains. If some are charging differently than others, it is the fault of the local USB charger.
The reason? Long lines have high voltage drop which is bad when your voltage is already low to begin with. Losing 1V when your voltage is 120V is barely noticeable. Losing 1V when your voltage is 5V is very bad.