A USB power supply steps up pc USB 5v to 12v for the Mobley
Designed to plug into your pc USB , and power the Mobley directly from the pc
To power the Mobley from 120vac buy the 120v adapter
The ad is saying do not use the USB adapter with a cheap 120vac to USB charge adapter
Use it Only with your pc
Best guess is the converter chip in the USB to 12v adapter is sensitive to voltage, and some of the cheap adapters are not well regulated
They worth with phones because phones have built in charge regulation to control the voltage
If you look at a cell phones battery yo will see it is not 5v
It is usually 3.7 volt, and the phone circuits keep the applied charge voltage under control
The USB adapter has no charge control circuitry
It is converting 5v to 12v
And to high an input voltage could damage it
