Sometimes even a well designed and assembled power supply can be dangerous because of defective components. Big Clive on Youtube does many teardowns of cheap electronics, and here&#x27;s one of a USB power supply that&#x27;s dangerous because of internal damage to the transformer:<p><a href="https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=3Hdn0MuCK_0" rel="nofollow">https:&#x2F;&#x2F;www.youtube.com&#x2F;watch?v=3Hdn0MuCK_0</a><p>Because this is an intermittent fault it&#x27;s possible that non-destructive testing would not find it.