Of all the things people worry about when travelling, the laptop is the safest. Nearly every laptop power supply made since the 1990s accepts 100–240 V at 50 or 60 Hz, which covers every grid on earth. What changes is the plug on the wall end — and sometimes the cable.
Check the brick
Look at the text on the power supply, not the laptop. If it says INPUT: 100–240 V ~ 50/60 Hz, you need nothing but a plug adapter. If it names a single voltage, it is an old or unusual unit and needs a converter.
Apple, Dell, Lenovo, HP, Asus, Acer and Microsoft all ship universal-input supplies. So do USB-C PD chargers, which is one reason a 65 W GaN charger has replaced the brick in most travel kits.
The plug, and the cable
Most laptop supplies use a detachable "figure-eight" (C7) or "Mickey Mouse" (C5) mains cable. That is useful: instead of an adapter on the wall, you can buy a local mains cable for a few pounds and plug straight in. It is tidier and avoids the wobbly adapter stack.
If your supply has a fixed plug, a standard travel adapter is fine.
Earthing
Laptops with metal bodies usually have a three-pin mains lead. In countries where only two-pin sockets are common (the US, Japan, Thailand), an adapter that ignores the earth leaves the case floating — which is why some people feel a faint tingle on a metal laptop in a humid country. It is not dangerous at mains voltage in a functioning device, but it is worth using an earthed adapter where one is available.
Voltage, wattage and heat
Laptop supplies are switched-mode and self-regulating: 120 V in, 19 V out, same as at home. They run slightly warmer on 50 Hz grids in some designs, but this is normal. There is no need to change any setting.
What about plugging in other things through the laptop?
Do not. Charging a phone from a laptop USB port in a foreign country is fine; running a mains appliance from a laptop is not a thing. And never plug a US-only power strip into a 230 V socket through an adapter — the strip's surge protection is often rated for 120 V only, and it will fail.