There are two types of PTs, so people get confused. The "regular" charge via USB PTs with batteries are, of course, not an issue. It's the direct-PTs (5v) that cause the issues (like the homemade ones you are talking about).
Sigh. You know, it MAY work. USB ports are protected (per the "tech savy" comments above) and the newer standards (3.0) are even more robust. That said, there are so many variations of equipment (old mobo's with 1.0 usb ports, laptops, netbooks, usb 2.0, usb 3.0...lots of chipsets) that it's just a good general recommendation
to avoid it.
hmmm. $15 passthrough versus $1500 computer... or for savy users $150 mobo and time to replace.
Just doesn't add up to me.
Good luck!
^^^^ this.
Also, understand that protected ports != (not equal) perfect safety. The 2.0 amp/10 watt draw, on/off/on/off/on/off with vaping still stresses the components and the mobo is a lot more expensive than a $10.00 wall wart IMHO. It's just cheap insurance. The low voltage others have mentioned is due to their particular port not putting out enough amps under load (thus it is stressed). 3.7 volts is either a battery powered PT (unlikely since 5v no-load), limiting circuitry, or only 1.2 amps from the port (voltage suffers). Many ports even have a 500ma per port limitation depending on the device and standard. You get the idea.
Also, a wall wart allows you to vape wherever there is an outlet (no computer required) so you should probably have one anyway.
So, if it works with your USB port, but not the wall adapter:
1) underpowered wall adapter (you need about 2.0 amps)
2) busted/fried wall adapter that is malfunctioning.
3) bad outlet?
solution: use proper outlet and/or replace the wall adapter for $10.00 or less.
