International electrical compatibility depends on more than the outlet shape. The device input range must cover the destination voltage, and frequency-sensitive equipment may also need to support the local 50 Hz or 60 Hz supply.
What 100–240V means
An input label such as 100–240V normally indicates that the power supply can accept nominal mains voltages across that range. The plug may still require a mechanical adapter.
Why frequency matters
Many modern electronic power supplies accept 50/60Hz. Motors, clocks and some medical or specialist equipment can behave differently when the supply frequency changes.
Single-voltage equipment
A device marked only for one voltage range must not be connected to an incompatible supply with a plug adapter alone. High-power heaters and hair appliances are often better replaced with destination-compatible equipment than used through a travel converter.