While I could be wrong, I’d think that with 2.1 amps you could power the laptop and have a bit left over for charging the battery. The laptop’s circuits though would need to be designed to allow that much input current through the USB port.
2.1 Amps in a USB cable is only 10.2 Watts. That is less than 65 Watts. There aren’t many laptops that can run a screen and a disk drive for less than 20 Watts.