Ramoroa brought up what I couldn't think of and didn't mention--the adapter is what converts the plug, the transformer (what I left out) is what converts the electrical current. I am not sure if a warmer would need the current converted--if you don't convert on some items, it will blow it. I think it has more to do with items that have moving parts, but I am not 100% sure. Electrician, I am not Edit to add: I found this blurb at a retailer to explain the difference between a transformer and a converter (converter what we call an adapter): North America operates on 110 volt electric current, where as much of the world runs on 220 volts and as high as 240 volts. So if you wish to use your U.S. 110 volt items overseas, your appliances will require a transformer or converter. Converters and transformers change electric current. Converters are designed to work only with electric appliances (for example, hot pots and hair dryers). Transformers are designed to work with electronic items that have a chip or a circuit (for example, camcorder recharges and radios AND electric appliances). Converters and transformers are available in different wattage combinations. Converters are available from 50-1600 watts. Transformers are available from 1-; 100 watts, 200watts, 300 watts and stronger. Your transformer will either step up and down the power (change 110/240 volt electricity into 240/110 volts) or step it down (change 220 volts to 110 volts) so you can safely run your appliance. The manufacture recommends you purchase a transformer that is 25% higher then the wattage you need. You should know that you will never damage your appliance with a higher wattage transformer, however if you buy one that is not powerful enough, it will not work.