I always see laptops come with larger bricks that have separate mains cable which plugs into the brick. Even if the adapter has some low power rating.

Example for comparison:

On the right is a standard laptop adapter.
Same price, same connector, same protocol, same power rating, far different size.

Why is that so?

Actually, the GaN adapter on the left also advertises itself as being meant for laptops, but by default, almost all laptops will come with something like the one on the right.

Or is it simply cheaper to manufacture while being sold for the same price?

  • flyingjake
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    25 days ago
    Watts are part of the electrical properties along with volts and amps. Laptop chargers have the same watts and volts but more amps. 
    

    This is incorrect, Watts (power) is the product of amps * volts. The formula is P = IV. Anything with the same power and voltage will have the same amps.

    The volume of power consumed would be Watts * time and gets you to capacity and usage units like watt-hours.