So the other night when I plugged my iPhone into a wall charger to charge, it started repeating the double-vibrate "I'm charging now!" notification. It was behaving as though it was being connected and disconnected randomly. It being used with a long third-party Lightning cable, I instinctively suspected the cable and ordered a new one and just charged the phone on my Mac Pro.
A few days later, after charging one of those external USB battery packs on the same wall charger, I tried a different, original Apple Lightning cord on the wall charger, and lo and behold, the vibrating resumed anew!
I pondered how to test the charger, and then stumbled upon a humble USB LED gooseneck lamp I have had for ages. I plugged it in, and the lamp started flashing!
Here's what it looks like:
For comparison, an identical charger in full working conditions looks like this:
Anyway, if anyone has suggestions/requests for investigation avenues before I chuck it, let me know!
P.S. If anyone can share with me how to embed the videos instead of links, please let me know, I couldn't find it.