Mirror: (I will get an Internet Archive link when I can, it's not behaving currently.)ĭell and HP adapters are almost always grounded. If you touch a floating common ground lightly enough, and the atmospheric conditions are right, you'll feel each rise of the 50 Hz mains as the resistance between the tiny contact point of your skin's surface and the electrically-driven pressure (touch) nerve endings changes. Whilst the current levels flowing through you into the air borders on submicroscopic, you're being exposed to 120 volts. Sure, its high resistance, but it is a conductive path that was not there before. So what causes the tingling sensation? If you touch the case (and thus, common ground) you, dear human, become the earth - current flows from the case into you, and through you into the atmosphere. There's not enough current to harm you, nor the electronics inside the device being powered by the SMPS. When the device's common ground is not connected to an earth, the common ground (which often includes the case, if it is metal) is energised to half the mains AC voltage, but at a very very high impedance. When the device's common ground is connected to an earth, it is maintained at zero potential, and the EMI gets dumped.
Here's the explanation for My Laptop Bit Me - The Shocking Truth by Enclydion:
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