4 ms·

The reason for that is that the adapter is not really grounded, but due to EMC requirements there has to be some AC path to ground. This is done by connecting t

by dfox 4y ago

The reason for that is that the adapter is not really grounded, but due to EMC requirements there has to be some AC path to ground. This is done by connecting the output ground to midpoint of input EMC filter and thus the output ground is weakly capacitively coupled to half of the line voltage. Most higher powered laptop power bricks have three prong plug for exactly this reason.

afandian 4y ago
Yeah I'm using a Macbook Pro power adaptor and an Apple Cinema display. Both have earth pins (UK plug). Somehow their 'grounds' disagree enough to ionize air!?
- bombcar 4y ago
  Are you plugged into the same outlet? Different outlets could be on different circuits which can be enough to cause a ground difference.
  - afandian 4y ago
    Yes, the plugs are next to each other. And a mains tester is happy with the mains output.