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I watched the video, which is produced by a recognised charity and gives a very timely warning to all pet owners about the dangers of leaving animals alone in the home with electrical devices still plugged in.
Regarding the problem with your puppy, I would think that unplugging devices is the best solution. However, when I was a teenager my mother had a rabbit (who found her, not the other way round!) and he had a habit of chewing electrical cables - whether we were in or out of the house at the time. We used to change cables when possible, but sometimes in an emergency we were forced to put insulation tape on the chewed cables, LOL! We put the wires under carpets or behind furniture, wherever possible.
The only solution in the case of your puppy would seem to be to only put down essential wires as you use them and watch carefully. When you are not there, then the only really safe solution is to unplug - or preferably remove any cables at floor level. Hiding wires under carpets or behind furniture should minimise the risk, too.
Ultimately your puppy will probably grow out of chewing things. It is a natural phase in growing up, which normally disappears as the dog matures.
However, if he persists in chewing wires later on he will need training in not chewing them. There are a lot of videos on YouTube about training dogs not to chew. I won't give links here, but it is easy to search for videos there.