On Apple's website has information about the dangers of non-certified zaryadok

In October 

this year, Apple has tested stands with Amazon, proposed as new. It turned out that more than 95% of them turned out to be fake.

2 weeks ago, Apple officially announced that 99% of counterfeit or Chinese zaryadok - unsafe. And yesterday explained why and how to verify originality.

For technical support official website said:

Some counterfeit and third-party power adapters and batteries can be manufactured in violation of technological standards and may pose a risk to users. To make sure you're using the official Apple battery when replacing the battery, we recommend that you visit the official Apple store or authorized service center. If you need to replace the adapter for charging your devices, we recommend purchasing Apple supply unit.

And it really is. Chinese chargers often do not meet technological standards and can harm not only the iPhone, but the owner's health.