If you touch the output of the Full bridge Rectifier, and the circuit is powered directly from the city power, does it shock you with every positive wave of the 120ac? How about a half bridge rectifier? Its only one diode, but what happens if you touch the other end of the output, and how does this guy not get shocked:
https://www.youtube.com/watch?v=sI5Ftm1-jik (2:00),
and how does switched mode wall adapters isolate the live wire? This is so confusing!
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\$\begingroup\$ This guy most likely isn't shocked because he works on an ground-free power supply (which is good practice for any lab work with mains voltage.) \$\endgroup\$– JankaCommented Sep 12, 2017 at 0:12
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\$\begingroup\$ 2:24 - 2:55. facepalm For the ones playing at home: don't. do. this. \$\endgroup\$– try-catch-finallyCommented Sep 12, 2017 at 4:41
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First of all, it is always good practice NOT to touch live power wires. In the case of the video you mentioned and, almost all appliances and power supplies, there will be an isolation transformer connecting the mains to the circuit you are touching.
For a single phase, there are live, neutral and earth wires, on the mains side. The neutral and earth wires will be connected together and, ideally, be at the same potential. If you touch the live wire, you will likely form a circuit to the earth and be shocked. If a 1:1 isolation transformer is in between, you'll just have live and neutral wires effectively with no direct connection to earth, and if you touch the live wire on the secondary side, it is less likely a connection to earth will be formed (it can still happen though so don't touch)
There is a good discussion of this here: https://www.soundonsound.com/sound-advice/crosstalk-readers-writes.
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\$\begingroup\$ Yes, but the switching wall adapter doesn't even contain an isolating transformer, according to the weight \$\endgroup\$– BinaryCommented Sep 12, 2017 at 1:19
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\$\begingroup\$ @SimonCheng Why would a switching wall adapter not have an isolation transformer? If they're not cheap junk from china, they will have an isolation transformer. They'll be a lot smaller than you're used to, but that's possible because they up the frequency much higher than the 60hz present on mains. \$\endgroup\$– hortaCommented Sep 12, 2017 at 1:48