For those who get the pop-up messages when plugging in the cable and the iPhone is not charging, I got a kind of a fix... Just plug in the cable, ignore the messages and turn off the phone. If you open it after a few minutes, you will see that it has been charged, even though nothing appears on the screen while turned off. You just have to do this each time you want to charge your iPhone and you have to keep it turned off for about an hour to fully get charged. Worked for my iPhone 5C, don't know for other i-devices. It's because I'm using a third-party cable (not the original Apple one, which I broke). I got the "not supported" messages before, but it was still charging. But since last iOS update, this is the only way I can charge my phone. Also, from what I've heard and read, an original cable could also show the same issues, so there's no point buying one.
Just remember: first plug in the cable (using a charger or a computer, doesn't matter), then turn the iPhone off.