Perhaps you saw the recent news about a woman in China allegedly electrocuted by a knockoff or otherwise third-party charger. And Apple, while certainly not directly responsible in cases such as this, is offering a discount exchange program to anyone who suspects they have a counterfeit charger. The company is under no obligation, of course, to do this, but they are to be commended for putting safety first. Apple may, however, be at least indirectly causing issues such as this with a complex Lightning cable design.
You might think that, given the standardization on USB chargers in recent years, that all of this wouldn't be a concern anymore. But the variability inherent in electronics design and manufacture should give us all pause. AC power is not to be messed with under any circumstances. Compromise here is never an option.
I also experienced a strange, if non-fatal, problem with a powered USB hub that I had been using to recharge my iPhone. The iPhone often wouldn't fully charge, and, even when it indicated a full charge, would discharge fairly quickly. I also noticed a bizarre checkerboard pattern on this display that would fade a few hours after be disconnected from the hub. I have none of these problems when I charge the handset with the tiny Apple cube transformer that comes with the iPhone.
Maybe there is indeed a sensitivity - yes, let's go with that - of some form related to the charging circuits in the iPhone. And maybe this has something to do with the Lightning cable, which, perhaps surprisingly, includes active electronics in the cable itself (perhaps one reason why it's so expensive). The conclusion I've come to is that it's not really a matter of the USB transformer alone, but rather the complex end-to-end system that's at work here. Apple is under no obligation, of course, to have their phone work properly or even safely with every possible USB power source. But perhaps a simpler design here would have eliminated any possibility of problems like these in the first place.