How many things do you know of where a voltmeter shows no voltage, but the device works fine?
I bought an auto/air laptop power supply for a friend of mine, and it was a good brand (Targus) and it's hard to imagine too high a voltage coming from a car, but since it wasn't my computer, I thought I should check the voltage before plugging it into his new laptop.
So, out in the car, I measured the voltage and got zero. Even though the light was on on the brick.
It turns out iiuc that the device is so fancy that it waits until everything is connected to decide what voltage to deliver to the laptop, and before then, there is no output voltage present.