Aren't primary and secondary still connected for EMI management (causing the "weird buzzing sensation" when touching metal parts of connected devices)?
About a quarter of the way down there’s a section called, “The charger's underside: many tiny components” picture with a red line on it. Below it talks about it and claims only optoisolators connect the two sides. Obviously the transformer also connects the two sides, but you know what I mean.
I don't have an answer to that question, only an educated guess. But I gave up on getting it a long time ago. I use the three pronged connector unless I'm plugged into something like an inverter.
Before that change I did end up throwing away a PSU that was causing tingling on my laptop. I don't know if that's a manufacturing flaw or damaged wiring.
The educated guess as to the mechanism is 'floating ground' (the white wire has a potential versus earth ground). It causes weird behavior in house wiring, particularly ones that have had iteration in their wiring (remodels, additions). Then there's the one where LED lights turn on even if the switch is off, but I think that's a separate phenomenon from floating ground.
It’s inherent to all class 2 PSUs (or really all PSUs without mandatory safety grounding, which is only safely possible as a class 2).
It happens even in a properly wired building without faults, since a class 2 PSU needs a path for EMI on the secondary side to be dissipated, and due to the lack of a dedicated ground, the only choice is to connect both phase and return to the secondary circuit via a Y capacitor.
A common downside of that is a stray voltage of up to half your mains voltage on any conducting surface of your device, but it’s harmless since it’s not capable of sustaining any meaningful current.
It's sad that for such high price you have this "weird buzzing sensation" (which is because it is not grounded properly), and that you can hear the buzzing sound too if you put your ear very close.
By definition you can't have grounding on a power supply without a grounding pin, unfortunately.
Apple's power supplies for MacBooks do have a grounding pin, but the default duckhead adapter they ship with usually doesn't leverage it, so you end up with a class 2 power supply and the buzzing sensation.
> that you can hear the buzzing sound too if you put your ear very close.
I've found Apple power adapters to be pretty good in that regard, unlike some third-party power supplies that I can hear across the room. If I can only hear the noise when I put my ear next to the supply, I can just not do that :)
