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A plug adapter changes the shape of the pins. A voltage converter changes the electricity. Confusing them is how a dual-voltage laptop charger is fine in Paris and a 120-volt hair dryer is not.
The argumentA travel adapter is a piece of plastic that maps one plug shape onto another and passes the wall's voltage through unchanged. A voltage converter (or transformer) changes that voltage. Almost every modern phone, laptop, tablet, and camera charger is dual-voltage (INPUT 100-240V) and needs only an adapter; heating appliances that list a single voltage, typically 120V, will take whatever the wall supplies if you only change the plug, which in much of the world is about 230V.
Why can my laptop charger travel with a cheap plug adapter while a hair dryer plugged into the same adapter would be a fire or a brick?
An adapter never changes voltage. If the wall is 230V, the device sees 230V, whatever the plug now looks like.
INPUT: 100-240V (often with 50/60Hz) means dual-voltage: adapter only, anywhere with mains in that range.
INPUT: 120V only means a converter or a different device. Hair dryers, straighteners, and travel irons are the usual cases, and a converter must be rated above the appliance's watts.
This is the electrical distinction. Choosing a grounded, fused adapter kit is a separate shopping problem.
The plastic block in a travel kit does one job: it lets a plug physically enter a foreign socket. It does not step 230 volts down to 120, it does not 'convert European power,' and the USB ports on the side of a universal adapter are a separate, low-voltage circuit. The AC socket on that same adapter is a pass-through. Whatever voltage is in the wall is what comes out of the adapter's outlet.
That is why a laptop charger and a hair dryer, plugged into the same adapter in the same hotel, are not in the same situation. The charger almost certainly says INPUT 100-240V on the brick and will accept either mains. The dryer almost certainly says 120V, will try to pull twice the current it was designed for, and will smell like a mistake within seconds. The difference is printed on the device. It is not a property of the adapter.
Mains voltage is not a local quirk. IEC 60038 is the standard that names the usual values. Most of the world delivers a nominal 230V at 50Hz to ordinary wall outlets (older national figures of 220V or 240V were harmonized toward 230V). The large exception is the 100-127V, usually 60Hz, band: the United States and Canada at 120V, Japan at 100V, and a set of countries in the Americas. Plug shape is a different standard. IEC's World Plugs reference lists types A through O. Type A/B can appear at 100V or 120V; Type C/F is the common 230V European pair; Type G is the UK's 230V rectangular-pin plug. Fitting the socket and matching the voltage are two separate checks.
Read the INPUT line on the power supply, not the voltage printed on the gadget body, and not the output line (OUTPUT 5V, 20V, and so on is what the charger sends to the device after it has already done its job). A typical phone or laptop brick reads something like INPUT: 100-240V ~ 50/60Hz. That range covers Japan through the UK. Pack an adapter for the pins. Leave the converter at home.
| Object | Changes plug shape? | Changes voltage? | What it is for |
|---|---|---|---|
| Plug adapter | Yes | No. Passes wall voltage through. | Dual-voltage chargers and appliances when only the pins differ. |
| Voltage converter | Sometimes includes plug faces | Yes, usually 230V to 120V or the reverse, up to a printed wattage. | Single-voltage heating tools, for short use, if you insist on bringing them. |
| Transformer | Usually no | Yes, via windings. Heavier, meant for longer or stationary loads. | A device that will sit on a desk for weeks, not a hair dryer in a suitcase. |
What does the device or its charger brick print next to INPUT?
Look at the brick, the nameplate, or the molded text on the appliance. Ignore OUTPUT.
Hair dryers, straighteners, curling irons, travel irons, kettles.
Converters are sold as if they were a second adapter. They are not. A step-down converter takes 220-240V and produces something near 110-120V. A step-up converter does the reverse. Both have a wattage ceiling printed on the case, and that ceiling has to sit above the appliance's draw with margin. A 1,800W dryer on a 1,000W converter is an overload, not a clever packing choice. Many inexpensive 'travel converters' are built for resistive heating loads and produce a modified waveform. That can be survivable for a simple heating coil and hostile to motors, clocks, and anything with a switching power supply. If the device was sensitive enough to need clean power, the converter in the travel aisle is the wrong tool; a heavier transformer is the right one, and at that point you should ask whether the device belongs on the trip.
USB ports on a universal adapter are a third category. Those ports contain their own small supply that takes whatever mains you feed the adapter and puts out USB voltage. They will charge a phone. The AC socket next to them will not protect a 120V appliance. Marketing photos that show a hair dryer and a phone sharing one 'universal converter' are mixing the two paths on purpose.
IEC 60038 (standard voltages) and IEC World Plugs, accessed 2026-08-12
The practical packing list follows from the labels, not from the destination's reputation. Phones, laptops, tablets, camera chargers, electric-toothbrush chargers, and most modern laptop-style power supplies: adapter only. A 120V-only heat tool: leave it home, buy a dual-voltage or local version, or pack a converter you have actually sized to the wattage. A CPAP or other medical device: read the specific input rating and the manufacturer's travel note; do not generalize from a phone charger. If nothing you are bringing is single-voltage, you do not own a converter problem. You own a pin-shape problem, which is smaller, lighter, and cheaper.
Adapter: shape. Converter: voltage. The USB ports on an adapter are not a converter for the AC socket.
INPUT 100-240V: pack an adapter. INPUT 120V: pack a different appliance, or a converter rated above its watts.
Most trips with modern chargers never need a converter. Heat tools are the exception, and they are the items worth replacing rather than converting.
It converts voltage for the USB port, which outputs USB power. The AC receptacle on the same body still passes mains through. A 120V dryer in that receptacle in a 230V country still sees 230V.
If the charger is already 100-240V, a converter is unnecessary. Putting a switching laptop supply on a cheap heating-load converter can add heat, noise, and a bad waveform without adding protection. Plug the dual-voltage brick into an adapter.
Many North American plugs will physically fit. A 100-240V charger will accept 100V. A 120V-only appliance will run under-voltage, which is a different failure (motors and heaters performing poorly) than the 230V over-voltage case. Read the INPUT line anyway; pin compatibility is not the same as voltage compatibility.
Sources and further reading
Defines the internationally standardized mains voltages. A 1997 amendment harmonized older 220/380V and 240/415V values to 230/400V; North American 120V systems remain the large exception.
IEC's country-by-country reference for plug types (A through O), nominal voltage, and frequency. Plug type is independent of voltage: the same Type A/B family appears at 100V in Japan and 120V in the United States.
Secondary compilation of national plug types and voltages used here only to illustrate that most countries sit in the 220-240V band while a smaller set, including the United States, sit near 120V.
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A plug adapter reshapes a plug so it fits a foreign socket; it does not change the electricity coming out of the wall. Confusing the two is the single most common way travelers damage a device or start a fire.
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