Have you ever noticed this small cylindrical module near the end of your laptop charger?
Yes. I'm talking about the same ugly blob that pops out at the posterior end of the cord.
While you might think it's useless, but computer geeks and technology freaks swear by it, because well.... It's kinda important.
The cylindrical device is known as a ferrite bead, which is nothing but an inductor (passive electric component) that suppresses high frequency noise in electronic circuits.
The ferrite bead isolates your laptop from electromagnetic noise, either from the waves that are picked up by the wire or from the existing noise in the AC-DC converter or the AC line.
This specific type of electronic choke employs the dissipation of high frequency currents in a ferrite ceramic that helps build high frequency noise suppression devices. These are sometimes called cores, blocks, rings or even EMI filters.