This topic may be obvious to electrical engineers but I though it would nice to share a personal DIY success story. A few days ago the power brick to one of my Logitech devices failed. The device was several years old and I couldn’t find a replacement power brick anywhere. The power specification for the device is 5V DC at 500mA and it takes a 3.5mm barrel jack as input. This characteristics are very similar to those of USB powered devices so I set out to find a USB to 3.5mm barrel jack adapter. Amazon sold one for $1.50 and I decided to try it out. The cable worked but was very short and flimsy (I didn’t expect much for that price anyway). Also, the barrel jack from the cheap cable didn’t fit snugly in the device.
The solution was to take the cord that came with the device (it was the right length and had a power jack that fit perfectly) and splice in a male USB jack at the other end. The cables inside a USB wire are color coded (Red is power, Black is ground) so once I matched those up to the barrel jack, the wire was good to go. A little solder and electrical tape to tidy up the splice and cheap 500mA USB power adapter for the outlet rounded out the project.