Orion sir have burnt my lip a few times using a wow carto and the passthrough in my car. Why it's always suggested to use a plastic drip tip with that set up, you're running at 5v volts on the pt compared to the ~4v on the regular batteries. Wow cartos can come in as low as 2.0ohms which is 12.5 watts. Can get the metal carto quite hot.
As for why you shouldn't use a pt on a computer (not the Zeus, but a straight pt) isn't the voltage but the amperage. Standard USB 2.0 ports are rated for 500ma (which is why the Zeus doesn't count, that's all it's charger pulls when using it as a passthrough), USB 3.0 900mah. There are some that run higher (have a 2a port on my computer) but still it's not worth the risk using a pt on it. You need at least 2 amps to run a wow carto on a pt. One of three things can/will happen from running it on your comp-
1.- Port will only put out whatever amp limit it's rated for severely limiting the performance
2.- You can burn out the port
3.- You can kill the motherboard and/or fry the power supply
Better to by an adapter rated for 5v/2a.
"I know that I am hard to love, I know that I ask for far too much, but we get what we ask for sometimes, and sometimes we miss the mark. We miss the mark..."- ilyAIMY "the MARC"