Apple has announced a recall program for an AC adapter that has proven to be a problem (six incidents have been reported). This is a three-pin adapter as used in the UK, Singapore and Hong Kong:
They can break and create a risk of electric shock if you touch exposed metal parts. This adapter with wall outlet was sold between 2003 and 2010 with Macs and some iOS devices, and was also part of the Apple Travel Kit
The Apple Travel Kit (35 €) is a set of adapters for frequent travelers. In the card describing this recall, Apple shows the adapter that may be defective and its replacement.
The first has a completely white background and no inscriptions, the second has a gray part and indications of approval. There are also differences in the thickness (the bad is bigger). An exchange procedure has been put in place.
In 2016 Apple had faced a different problem on the bottom but also affecting an adapter, sold over a period of 12 years.