The voltage rating can usually be found on the laptop's power supply/transformer unit, which can be attached to the power cable, to the plug itself or sometimes built in. If it says 110-240v, 50-60Hz, it should be OK for both USA and Europe. If the voltage is printed on the power cord itself, you can't be sure that isn't just the power cord rating and not the power supply rating. So, check the power supply unit!