Since I only have Compact Pro, can't be sure about other model but I don't think is different.
OTG standard is 5V
Agree,lightning plug contains only some chip to enable OTG function on Apple devices. And micro USB just a short on pins 4-5 to enable OTG in devices,also USB-C variant,required 5.1K resistors to enable same OTG function.
No voltage regulator inside any plug,lightning,microUSB or USB-C
5V from USB or OTG go to step down regulators,on board.
One TPS62560 (2x3 pins package on left side) and another one is that 2x2 pins on right side of LPC.
https://www.eevblog.com/forum/repair/seek-compactxr/After I added missing 337S3959 on Android version I can use it on iPhone.
And iPhone supply 5V on OTG.
Look at chain iPhone OTG cable,USB volt-amper meter,USB-C female adapter,micro USB to USB-C adapter.