I have a cheap car inverter that has AC and DC output. The instructions dont say how much amps the USB dc 5v out has.... I have a Fluke meter and it has DC amps.
Where do you put the leads to check a USB plug for amps..????

 

If it is the Black & Decker inverter, it uses a series resistor with a zener to ground to give you the 5 volts. It isn't a physically large zener so I wouldn't expect much in the way of current out of the USB connector. Just had mine apart but didn't check the resistor value. It does get warm to the touch with a 15 volt input.

 

USB from a PC is about 500mA - that's a pretty standard value. I would hazard a guess that's about what it puts out.

I wouldn't plug an Apple iPad into it, those iPads need about 1Amp.

If you want to really test it, here are the pin outs for a USB port

http://pinouts.ws/usb-pinout.html

 

the rep said its 1 amp. Its a Cyberpower BU150 car inverter. It works good but noisy fan.