It can be used to charge 2 devices at the same time, in this case the voltage is the same for 2 but the intensity adds.
It allowed me to see that one of my chargers were far too high voltage, 5.25V and could harm the support unit, especially none has an internal removable battery.
He also allowed my to check it ny was no tension on one of the 2 USB ports of a charger that I have recently bought.
Always impeccable service, packaging, mailing speed, etc ...
