(I&#x27;m not an EE, so if anyone knows better?)<p>Oddly, never had the same problem with a phone USB charger. Which is the opposite of what you&#x27;d expect: the USB chargers seem to be entirely solid-state, using flyback transformers[1], while the larger power adapters have room for a real wire-wrapped ring transformer[2], which <i>should</i> be providing better electrical isolation. (I would never expect to be shocked by dirty power <i>coming through</i> an induction ring.)<p>[1] <a href="http:&#x2F;&#x2F;www.righto.com&#x2F;2012&#x2F;05&#x2F;apple-iphone-charger-teardown-quality.html?m=1" rel="nofollow">http:&#x2F;&#x2F;www.righto.com&#x2F;2012&#x2F;05&#x2F;apple-iphone-charger-teardown-...</a><p>[2] <a href="http:&#x2F;&#x2F;www.righto.com&#x2F;2015&#x2F;11&#x2F;macbook-charger-teardown-surprising.html" rel="nofollow">http:&#x2F;&#x2F;www.righto.com&#x2F;2015&#x2F;11&#x2F;macbook-charger-teardown-surpr...</a><p>But if it is the device itself that was faulty, rather than the input power, it&#x27;s a different story; in that case you <i>want</i> at least <i>some</i> valid ground path, and complete isolation is bad (because then the device will ground through you, obviously.)<p>Maybe it&#x27;s just that the power adapter block has a separate ground path and expects to ground it into a dedicated ground pin (and, I guess, leaves the ground pin disconnected when a two-prong adapter is connected? That seems wrong-headed), while the USB chargers, made to assume two-prong usage, mix ground with positive.