I have read articles written by people who have torn down and analyzed Apple power adaptors for the iPhone/iPad and they have been VERY impressed by the very high level of sophistication and protection in those gadgets.
I have read articles written by people who have torn down and analyze
non-Apple power adaptors for the iPhone/iPad and they have been
appalled at the shoddy workmanship and unsafe circuit design in these gadgets.
Many non-Apple chargers claim to be UL-approved when they in fact are not. Others don't even bother, knowing that almost no one will even think to check for certification.
Non-Apple chargers are so dangerous that for a while Apple had a buy-back program, wherein they would take your non-Apple charger off your hands in exchange for a discount on a genuine Apple charger.
See for example
this and
this. It's not just that the workmanship is shoddy and the parts inferior. It's that there is no attention at all paid to keeping the high-voltage input away from the low-voltage output. It would be one thing if the inferior products simply didn't work, but it's quite another that they can kill.
A friend's daughter came back from the flea market and proudly showed off the lovely pink iPhone earbud/charger pair she had bought for $3. Having just read articles similar to the above I knew what to look for. Her charger didn't even claim UL-approval. The good thing is that Apples takeback program was still in effect, and she wound up with a genuine adaptor at below normal list price.
I won't say
all non-Apple chargers are dangerous, but I will say I wouldn't even consider one. The risk is too high. I'm not going to put my life in danger to save a paltry few dollars.