So not so universal after all.
Let's expand on this a bit, USB On-The-Go (USB OTG or just OTG) specification has been around for a long time. It allows USB devices, such as tablets or smartphones, to act as a host, allowing other USB devices, such as USB
flash drives, digital cameras, mouse or keyboards, to be attached to them. As an example, a mobile phone may read from removable media as the host device, but present itself as a USB Mass Storage Device when connected to a host computer.
USB OTG introduces the concept of a device performing both master and slave roles – whenever two USB devices are connected and one of them is a USB OTG device, they establish a communication link. The device controlling the link is called the master or host, while the other is called the slave or peripheral, and as of USB 3.0 they can switch roles with a bit of code. Not all cables sold as OTG will work, mainly because of inferior construction... Ask me how I know.
Some YouTube videos that show how to build an OTG cable are wrong, while they have the correct pinout the resistance and capacitance would not work in the USB 2.0/3.0 standard. One video claims to get 3 amps through the cable which USB 2.0 limit is .5 amps while USB 3.0 limits amps to .9, good luck on trying to get more than that from a laptop or tablet.
DJI allows your phone or tablet to be charged via the RC which may be a good idea for some pilots, but since my phone is almost never at a low charge that would affect the flight I'm not a big fan of it.
Hope this helps,
Cheers!