M Philbrook wrote, on Mon, 30 Nov 2015 17:08:19 -0500:

I did the math and from my point of view, it looks correct.

You make a fair enough point of where things are going, which,
for this issue, is simply to *understand* what is happening.

I think the melted cable is merely a bad cable (with a low
resistance short between internal wires perhaps).

I don't (yet) understand the 40Watts of "power".

Going only by the printed specs, if that 40W is stating the
input power, wouldn't that be double that (at 100VAC rms times
800mA rms)?

And, if the 40W is output power, there's no way that 5VCD times
6.8Amps is anywhere near 40W (it's 15% less, which is a lot).

So, if your numbers matched the 40Watts (whether that's input
power dissipation or output power), if you show the math, it
would be better understood by me.