Hi, we are sorry for the inconvenience. It is true that the charging speed would be getting slower when this Anker's 7 port USB 3.0 USB 3.0 hub with 36W power supply is connecting with a computer.
When the hub isn't connecting a computer, this 7th port provides 5V/2.1A for the charging purpose. But when a computer is connected, part of the current is used for data transfer purpose, so the 7th port can only charge a device at 5V/1.5A.
Therefore, we are sorry it is not possible to get the quick 2.1A charging to work when the hub is connecting with a computer.