Dell DA300 User Manual page 11

NOTE: When the mobile adapter is connected to the 5V/1.5A USB-C port
on your computer only one of the USB-A and USB-C ports will work.
For example:
•
When a peripheral is plugged in to the USB-C port on your mobile
adapter, the USB-A will be disabled.
•
When a peripheral is plugged in to the USB-A port on your mobile
adapter, the USB-C will be disabled.
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