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SESK: Stuff Everyone Should Know · sesk.info/wt-dual-voltage-labels

A charger labeled 100-240 V usually needs what extra gear to work abroad?

A dual-voltage charger usually needs only a plug adapter.

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  1. A voltage transformer
  2. Just a plug adapter, if the plug won't fit ✔
  3. A second battery

Why: A 100-240 V label means the device handles both low and high mains voltage. Japan's tourism board notes dual-voltage hair dryers, irons and shavers work anywhere in Japan.

Huh, didn't know that: Single-voltage appliances are different: in other cases a step-down transformer is needed to convert the voltage.

The dad joke
100-240 V means the charger is bilingual in electricity.
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References

Answer: Just a plug adapter, if the plug won't fit. A 100-240 V label means the device handles both low and high mains voltage. Japan's tourism board notes dual-voltage hair dryers, irons and shavers work anywhere in Japan.

  1. Travel advice for electrical appliances (Electrical Safety First) www.electricalsafetyfirst.org.uk/safety-advice/travel-advice
    A dual voltage rated appliance will display (for example) ‘INPUT: 110-240V’ on the body of the appliance or its power supply.
    Checked 2026-10-12.
  2. Travel advice for electrical appliances (Electrical Safety First) www.electricalsafetyfirst.org.uk/safety-advice/travel-advice
    This means the appliance can work with any supply between 110V and 240V.
    Checked 2026-10-12.
  3. Travel advice for electrical appliances (Electrical Safety First) www.electricalsafetyfirst.org.uk/safety-advice/travel-advice
    If your electrical appliance (or its power supply) is “dual voltage rated”, you won't need a voltage converter or transformer.
    Checked 2026-10-12.

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