olf2012:
The reason for charging problems does not lie with the power lines, but with the data lines. The signaling voltages are easily distorted by corrosion, loose contact springs etc. then the signaling is broken and the phone adjusts the current to some false value.
Ah, yes, that's more likely.
As the data lines carry only very tiny currents their contacts will not be self-cleaning like the high
current contacts. Thus oxidation/corrosion can build up.
In case people were wondering about resistance of a cable changing as it wears out, think about the
fact that the cable is many strands in parallel that are all in contact along their length - so any weak
or broken strand will be worked-around with only a very short section of higher resistance, making
little difference to the overall cable until the last strand breaks and arcing happens.
I recently had a notebook charger cable fray and fail, and the symptoms were a sudden lose of charging.
Some arcing visible through the black pvc cable sleeve when wiggled... (The cause was a completely
rigid strain-relief sleeve, ie a sleeve that looked like a strain-relief sleeve, but molded from the same
rigid plastic as the connector body - thank you Toshiba!)