I recently got a desktop LED lamp, and I feel a "strange" slight vibration when touching the metal case. I found that other devices also have high voltage on their case.
What is the reason/trade-off to design the PSU that way? Are "real" transformers inefficient? Even if it's harmless, why is the high voltage connected to the metal case, and not just through insulated wires?
When I turn the lamp on, the setup in the picture measures
the power line (220V) 214Vpp (59Vrms). When I also touch the metal case, the voltage drops down to around 30V.