mm wrote:
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.
Hi,
If the adaptor has a built in series regulator, no load, no vvoltage.
Parallel regulator has current sink. Without load it'll show voltage.