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?
Voltage is the same but wattage is not.
Most of your phone chargers will be 65w or less while a laptop isn’t going to charge on fewer than 100w most of the time.
Which is why I said power rating as opposed to voltage or current.