nospam wrote, on Mon, 30 Nov 2015 12:45:25 -0500:

probably what it consumes, not what it outputs.

It can't be the input because 100-220VAC times the maximum stated
800mA input current is 80 Watts (give or take) input, which would
be about right assuming 50% efficiency.

usb devices initially get 100ma and then request how much power they
really want. the charger responds with how much it can supply.

That is interesting. So, when I plugged in the iPad, it "asked" for
100mA, and then it asked for more, so the charger gave it more?

But, then, why did the cord melt?

some non-compliant devices ignore the negotiation phase and either
output whatever power is needed and/or the device uses whatever is
available. that's probably the case here. however, that alone is not a
problem.

I understand that a current "source", which is the charger, is just a
source of current (sort of like being a big tank of water); it's not
going to "push" that current into the current "sink", which is the
iPad at any rate more than what the iPad "asks" for.

So, I'm assuming that the cable is bad (maybe pins are shorted, for
example, between power and ground).

But that still doesn't explain why the device says it's both 40Watts
output and that its maximum output is 6.8Amps at 5VDC.

That's not even close to 40 Watts (it's 15% off).