When you're under your desk, pulling at the power strip, all those little black cords and transformers look the same. Skip tags that can fall off and labels that peel; identify your cords and transformers with a metallic Sharpie.
Frugality blog Frugal For Life shares a simple tip for using a sharpie for cord marking.
The minute I pull the new item out of the box, I mark the plug. This way, if the cord isn't paired with the item, I will be able to find it among the other cobweb of cords. Metallic silver is perfect for all those black cords and red or black for other cord colours.
This is also very handy for when you have cords plugged in to a 12 count surge protectors. Don't want to unplug the tv, but need to reboot the cable box? Once you get the right one, write on it C.B in a small corner and you'll be ready for when the phone tech tells you to unplug the power to your cable box to reboot it.
Organizing Electric Cords [Frugal For Life]