Reddit post shows what happens when the ASUS ROG Phone is connected to itself
The ASUS ROG Phone technically has a total of three USB type C ports: a normal charging/data port, and two others in series along the side of the phone. The additional ports are present to connect to a range of optional branded accessories for the phone, such as its external fan or controller. In a world of dwindling 3.5mm jacks, this is possibly a viable direction for smartphone design in the future. The Redditor kx11 decided to find out what happens when you connect one of these ports to another. The result: the ROG phone can apparently power itself.
When the 'normal' USB port is connected to one of the serial ports via a male-to-male Type C cable, the ROG phone's LED light is activated and the UI responds as though the device is charging. However, there is no reason why the phone would actually accumulate charge as a result of doing so. The video showing the ROG phone connected to itself does not last more than a minute, making it impossible to eliminate this possibility.
The 'self-charging' phenomenon is most likely no more than a software glitch: a similar video made by Android Police also shows that the device sees itself as USB storage when auto-connected in the same way. Then again, it is something for ASUS (and possibly Android) to think about for next-generation updates and devices.