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Question:

What is that black box on power cables?

On my power cable, (the thing that plugs into the wall, and laptop to charge it) well in the middle of the cord, there is a rectangle black box. What is it called, and what is the purpose of it?

Answer:

its a transformer to cut the mains plug voltage down to the same voltage as the battery which will be around 16volts to 20 volts for a laptop,the desktop PC will have the same transformer built into the tower casing beside the fan,but you just cannot see it, and there will be a voltage selector switch for the country you are using it in ie-UK =220-240volts, USA=110 volts or similar,both the laptops and desktops use the same internal operating low voltages,and mains voltage would fry everything inside ,that's why they are fitted with the transformers.

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