Answer: There are number of factors to consider.
1. Voltage source - usually a given with USB at 5v DC.
2. The amount of current your USB port can deliver - more is better. This will also affect the current draw of the item you are trying to power.
The voltage of the item you want to power: 9 or 12vDC
4. As noted above, the current draw in amps
If you are directly providing power to the item, then the current draw will be critical.
I believe the max output of the adapter is 2Amps at 9v or 1.5A at 12v. If the draw of the equipment is more than that, it probably won't work. And if the USB port can't provide that current, ditto.
If you are charging a battery in the device while using the device, you may have a little more leeway.
I am using a portable battery pack(little bigger than a cig pack) that can put out 5v DC 2.1A of the USB port and convert to 12v DC at 1.5A to continually charge a portable DVD player while running it. I test drove this setup and seems to work Ok.