Most laptops are set-up to run on different voltages. What kind of laptop?? The wall plug portion of the charger / adapter can be bought from the computer company.
Are you sure that your current transformer doesn’t already accomplish this? Check the box that’s attached to your 110VAC power cord, and see if there’s a UL label on it that already shows it to be capable of handling inputs from 110 to 220 VAC. (VAC = Volts, Alternating Current)
I haven’t seen a laptop since my first one (before 2000) that didn’t handle the full range.
As per @Tropical_Willie most AC units for laptops can do both. Read the fine print on the back of your AC unit. Notice one end of the cable is removable, you could put a different cable (Euro etc plugs). The AC will automatically adapt if it’s supported.
As has been mentioned, check the bottom of your laptop as well as the transformer box on the power cord. Most laptops can switch automatically and computers usually have a manual switch on the power supply allowing you to adjust for the different voltages. My laptop is a bit old, it’s from 2005, and I use it when I’m in Europe with no problem. All I need is a plug adapter.