True, any USB2 port by definition should be able to deliver 5 volts at 500 mA or less. And an Ego charger is typically listed as having an input requirement of 5 volts and 500 mA, with output at 4.2 and 420 or so mA. On paper, everything looks good.
And as long as everything works properly, no problems.
It's if something doesn't work properly that concerns me. If it's one in a million, well, I don't want to be that one.
Today's hard drives are much improved over when I started with computers. (Well, that was actually well before hard drives...
) But I back up my files. Almost religiously.
To me, the peace of mind in knowing that my data is safe, and that a flaming charger won't touch my computer, is well worth the wall wart. And if I want to use something as a pass-thru, the wall wart can plug into the surge protected power strip next to my CPU.
Murphy was an optimist.