Dell Latitude 3390 2-in-1 Owner's Manual

USB PowerShare is a feature which allows for external USB devices (i.e. cellular phones, portable music players, etc.) to charge using the portable system's battery.

Only the USB connector with a SS+USB+Battery--> icon, can be used.

This functionality is enabled in the system setup under the On Board Devices heading. You can select how much of the battery's charge can be used as well (pictured below). If you set the USB PowerShare to 25%, the external device is allowed to charge until the battery reaches 25% of full capacity (e.g. 75% of the portable's battery charge is used up).