Hi,
If you look at the construction of the plugs, the contacts are sliding surfaces, the thickness of which is very very thin.
I have a similar cable and I believe from the way it plugs in so easily, compared to a new cable that charges well, that the contact surface has worn down to be very, very, very,very thin.
They have to wear out sometime and with smarty phones needing to be charged every couple of hours, the plug will wear out.
Sorry I have a proper mobile phone not a smarty-distraction people killing phone, 2 to 3 days on its battery. cable is 5years old.
Tom.. 