Product review (1 stars): It's a dud, unfortunately
Was really hoping this portable car humidifier/computer tabletop humidifier would work out, but alas it didn't.  It leaks.  Took it on a road trip, driving mostly on flat freeways, and for some unknown reason, it kept leaking into my cupholder, where it was sitting.  Put water in it well below the 'max fill' line.  Car didn't break suddenly or go over any major bumps.  It just leaks.  I think from the seam about 1/3 down, and then slowly drips down the outside.  I found a large clear plastic cup, and placed it inside that, for the rest of the journey.  The water continued to accumulate in the cup.  There were also some strange blue debris floating in the water.  Couldn't figure out what they were.
Also, even though I used it in a very small confined space, a sport sedan car, it didn't seem to improve the air quality or humidity level.  It was extremely dry outside... probably less than 30% humidity, but it did not make the air inside the vehicle more comfortable.  I suspect it's because it's a cold water system.  It does not heat the water.  Sometimes it also emitted a strong ozone smell.
The car power supply adapter worked fine.  It has a USB option as well.
I don't know if another similar product would work better.  But this one's a dud.  I returned it and there were no issues with that.  Amazon makes things very easy.