Why do the boxes on the power cords for laptops get hot when they are in use?

Q: When I charge all of my laptops their boxes that are in the middle of the power cords get really hot. But if I were to leave it plugged up and not have them connected to the laptops they remain cool. Is there a reason for this?

A: power to charge your laptops battery is serging threw the box and is stored there to slowly seep out to the battery so it is not to over power the cord and battery.

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