How to Use USB-Powered Devices on Your Laptop
Quite a few USB doohickeys are self-powered. That is, they draw the electricity that they need from the laptop's USB port.
The downside to this is that it sucks up even more of the laptop's precious juice even faster. The good news is that you don't need an extra cable, power supply, wall socket, or battery for that device. USB-powered devices are also more portable because you don't have to worry about taking along power cables or batteries. Anything that lightens your load is good.
When you’re looking for a USB peripheral for your laptop, get the USB-powered version.
Most flash memory devices are USB-powered.
Those cooling fan pads you can get for your laptop are also USB-powered.
Not all USB ports provide the proper power to run some USB-powered devices. Generally speaking, you must plug the USB-powered device into the laptop itself or into a powered hub for it to work.