ADP Device requirement

USB 2.0 Specification, Section 7.2.4.2 

The USB 2.0 specification have an ECN that require device to have a capacitance of at least 1F in order for host with ADP feature to detect the device.

ADP detection is described in the USB 2.0 OTG & Embedded Host specification.

This ECN ensures that all USB peripherals have a detectable change in capacitance on VBus when they are attached. This ensures that OTG devices and Embedded Hosts can detect attachment of peripherals in the absence of VBus. A USB device is required to expose a capacitance on the VBUS pin of its connector of at least 1F. Make also not sure the capacitance exceed 10F otherwise the product will fail the inrush test.

Beware that many self-powered device not meet this requirement. So make sure that you have at least 1F capacitance over Vbus and GND when going for USB-IF compliance.