# Can 120V adapters function when supplied with 240V?

## Main Question or Discussion Point

Hi,

It is generally accepted that to use electrical devices in countries with AC voltages different from yours will require a separate adapter. But what actually happens in the adapter that renders it unuseable in another country?

Let's say we have a 120V AC to 12V DC adapter. I can't be sure, but I believe what it does is flip the bottom half up, step down using a transformer, then smoothen out the waveform using capacitors.

Now, let's say you are in a place with 240V AC wall, and you plug that adapter into the socket, does it output anything at all? Since the functions within the adapter itself are somewhat independant of voltage supplied, is it right to assume that this adapter will convert 240V AC into 24V DC?

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godchuanz said:
…Let's say we have a 120V AC to 12V DC adapter. I can't be sure, but I believe what it does is flip the bottom half up, step down using a transformer, then smoothen out the waveform using capacitors.
Not quite, step down-flip- smooth. There are other ways to get 12vdc from 120vac and it can be done without a transformer.

godchuanz said:
Now, let's say you are in a place with 240V AC wall, and you plug that adapter into the socket, does it output anything at all? Since the functions within the adapter itself are somewhat independant of voltage supplied, is it right to assume that this adapter will convert 240V AC into 24V DC?…
As someone stated in another thread you will most likely let out all the smoke the manufacture put into it.

What will happen depends on the design, but the 12vdc is usually the result of a solid state-regulating component that will attempt to maintain the 12vdc despite input voltage variations. If the device is designed for a specific function, say a power tool battery charger, component-reducing shortcuts may be taken to reduce manufacturing costs.

In short, do not plug a 120vac device into a 240vac source.

...

If it says "universal input 85-240 VAC" then it will work but it will still
put out 12 V.

Otherwise, don't do it!