Really nothing to do with arduino but I know someone here can answer. I live in the US and was in Europe last week. I took a voltage converter which converts Europe's 240V to 120V. On top of the device there was a switch which allowed 3 wattage settings. What is this switch doing internally? What is it doing to change the available "watts"? It seems like 240 to 120 is fairly straightforward and you could draw up to the max of the unit. It didn't make sense to me that there was a switch. Can someone explain?
Something to do with limiting the blast radius for higher wattages?
These type of converters have two different type of converters built into one unit. At LOW (up to 50W) setting, it uses an AC transformer to converter 220V sinusoidal waveform into a 110V sinusoidal waveform. This is the best approach for a voltage converter and works well for small electronics. However, to handle higher wattage the AC transformer would need to be much bulkier and heavier. Thus, at HIGH (1600W) setting, this converter simply uses a solid-state switch inside to chop off part of the input 220V sinusoidal waveform causing a highly distorted output waveform which is far from an 110V sinusoidal AC. A completely resistive appliance (such as travel iron or water heater) will work just fine regardless of different voltage waveform. But, do not attempt to use an an electronic appliance such as laptop, battery charger, DVD player or curling iron with this distorted 220V waveform, it will damage the item and the converter.
Probably the best thing is to avoid "converters". What are you using it for? It would be better to get a 220V phone charger, or a 220V power supply for your computer, etc. (with plugs/cords for whatever country you're traveling to).
A "good" converter is usually going to cost more than the proper power supply, mainly because they are manufactured & distributed in smaller quantities and sold as a specialty item. (although theoretically you could use the converter on multiple devices).