There's a lot of el cheapo/economy units out there that still have the input voltage selector switch that you have to be aware of, like
this one with the little red switch on the back..But most modern/decent units auto-detect and auto-switch..If the unit does not have a voltage selector switch, then it auto-switches within the voltage range shown on the sticker..With EVGA units you're good to go, no worries.
The wall cable can be different as RJ said above..So you could take the unit to another country that uses a different plug/voltage and just buy an input/wall cable from just about anywhere.
Many other electric things these days auto-switch too..Like hair dryers, electric razors, laptops, TVs, phone chargers, on and on, and will normally always say on them somewhere what the input voltage range is..Many hotels, internet cafes, airports and public places will have universal wall sockets that will accept different plug styles from different regions.