You are bored, and decided to browse eBay to see for new and interesting items. After a while you see a small 220V USB charger intended for the iPhone. The first thing you see is it is quite small, and does not have wires, only a USB socket, so it will be very easy to transport while traveling. And it is quite cheap, so you order one.
About two weeks later the small charger arrives to your home. You take it out from the envelope and gets fascinated about how small it is. So you grab a USB cable and connect your phone to the charger and the charger to the mains (220V). The phone gets into charging state, so you are happy.
But in less than 30 seconds you heard a big explosion and your house's MCB is activated. You smell like burnt, and you see some smoke coming out your new eBay charger:
In Spain we have a saying for this: Cheap things are expensive (Lo barato sale caro).
Fortunately, the phone survived.