After experiencing a notable shocking type sensation after coming into skin contact with my laptop and phone (both metal and plugged into their chargers), I decided to probe the chassis of both devices to discover a 50Hz 120V transient...
To investigate this further, I directly recorded the voltage from the grounds of the charger connectors to find the same transient. Swapping between two different laptop and two different phone chargers, all permutations yield the a large AC signal from their grounds. That said, swapping between a 10W to a 5W usb charger did drop the difference to 60V between laptop and usb charger grounds.
I’ve even checked the sockets to ensure that its not a wiring problem, and sure enough the earth, live and neutral are all where they should be and connected properly. N.B. I’m in the UK, so 240V outlets.
This is quite baffling to me since not only are the voltages produced by the charging circuits direct current, but neither voltage exceeds 19.5V! Any explanations/diagrams to explain this would be fantastic!