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Whether you're using a cheap $10 charger or something that costs an awful lot more, the modern USB charger is simply an amazing bit of tech. It may look like just a box plugged into a wall outlet with a cable going to another box. But behind the scenes, there's a lot going on.

The moment you connect a charger to your device -- whether it's a smartphone, tablet, laptop, or power bank -- the charger wakes up, and the two gadgets quickly negotiate the best and safest voltage and current combo to use before getting on with charging. Then, both the charger and the device being charged continuously monitor voltage, current, and temperature to ensure the charging is safe and nothing blows up or catches fire.

Also: 10 useful cables and connectors I use everyday (and they're affordably priced)