The objective of this instructable is to share a CONCEPT. With this concept you can likely create a lot of projects to meet your needs.
The photo shows the completed book light project.
Step 1: Step 1: the Power Supply, a 5.0 Volt DC Cell Phone Charger.
1. A standard computer USB port includes a 5.0 volt DC power supply for accessories. This means that any computer accesory that plugs into a USB port runs on 5.0 volt DC power.
2. Many cell phone chargers supply 5.0 volt DC power.
OK, that is really all I have to tell you, the opportunities are obvious: if you have an old computer accessory you would like to use but don't want to depend on powering it with your computer USB port, you can connect it to a 5.0 volt cell phone charger.
See how I did this to make a book light.
First look for an old cell phone charger that has a 5.0 volt DC output; it will be shown somewhere on the charger, likely near the plug.
Step 2: The 5.0 Volt DC Accessory
I chose this goose neck LED computer key board light I no longer used, and cut off the USB plug. I then connected the wires from the charger to the two wires on the LED light. It is often necessary to get the polarity correct, on a LED device the + has to go to the + or it won't work. I then added a simple rotary on-off switch and scrounged the clippy thing you see in the photo that holds the light to the book. The clip (I think it was meant to hold sunglasses to a car sun visor) was attached using hot melt glue. You could adapt anything that has a spring like clip.
The book light works great.
I have a pile of chargers from previous cell phones and other gadgets (Walkman, etc). Some are 12 volt DC, which make a good power supply for 12 volt applications. But be sure to use only a 5 volt charger for powering a device with a USB plug.