Apple is offering a free exchange for certain of its European USB power adapters:
Apple has determined that, in rare cases, the Apple 5W European USB power adapter may overheat and pose a safety risk. This adapter came with iPhone 3GS, iPhone 4 and iPhone 4S models shipped from October 2009 to September 2012 in the countries listed below. It was also sold as a standalone accessory.
To learn more, visit Apple’s official adapter exchange page.