I plugged my tablet's USB OTG cable into the Vado 3.0 display, while mounted to the bike, and battery turned on (and lights turned on, I didn't try with the lights off), and it started charging my phones.
The Vado end of the cable goes in "upside down" with the USB logo underneath (the wider edge of the plug on the top).
The phone, a Samsung Ace 4 Lite, said "connecting as a media device" (or similar) and started charging. I didn't leave it more than a minute to see if the battery actually went up.
My other phone, an old Samsung candybar thing, showed the same connect options as when connected to a PC, and then started charging.
So some Vados will charge some phones.
My tablet USB OTG cable is USB micro-B plug at one end and USB Type-A socket at the other end, so I need another phone charging cable plugged into the socket to connect the phone, but that's probably not significant.