Apple may make great USB chargers, but they have certainly cut corners and shirked responsibility when it comes to the rubber insulation of their Lightning and (MacBook) MagSafe cables.
I've brought my frayed MagSafe charger, which has degraded to the point that it's been staining everything blue, to an Apple Store Genius Bar multiple times, and the Geniuses (in multiple countries) keep saying that it's my fault that the insulation degrades over time, and that such "wear and tear" is not covered under warranty.
I've brought my frayed MagSafe charger, which has degraded to the point that it's been staining everything blue, to an Apple Store Genius Bar multiple times, and the Geniuses (in multiple countries) keep saying that it's my fault that the insulation degrades over time, and that such "wear and tear" is not covered under warranty.