Spaghetti is a tasty and cost-effective meal; however, if you're not careful, your wires and cables have the potential to turn into it. When you acquire multiple pieces of equipment, you can end up with a messy tangle of AC adapters before you notice. It's always a good idea to keep them organized with Rip-Ties, but I've found it can be even more helpful to label them with tape and magic markers. Here's how I do it...
AC adapters and power supplies are very rarely labeled by the manufacturer. If you take a few minutes to label them yourself, there will be no mystery as to which power supply belongs to which piece of equipment in your arsenal. This will make it easy to locate the proper power supply when several are in storage, and it will also make it clear as to which piece of equipment is plugged into which outlet when you're using your equipment.
This is a painfully simple practice. The most difficult part is motivating yourself to do it. I make a point of labeling my AC adapters in the very beginning, right after I open a brand new piece of gear.
Step 1: Find an open surface on the AC plug. I find that the wide, flat side of the plug is a good choice because it doesn't get handled as often. Tear off a little piece of tape and affix it to this surface. I use white paper Permacel Shurtape. It sticks pretty well and it's easy to write on, but it also can be pulled off without leaving adhesive residue behind.

Step 2: Carefully cut the tape so it's flush with the edges. This will keep it from getting pulled off accidentally. I find that the little scissors on my Leatherman Wave are a good size for this task.

Step 3: With a permanent marker, write something on the tape that identifies which piece of gear the power supply is supposed to be used with. In this example, the power supply is for my RME Fireface UC, so I wrote "UC" on the tape. This particular power supply has two parts, a power brick and a removable AC plug. Note that I also used tape and marker to identify the power brick. This is essential for proper organization.

It's a really nice feeling to have all of your AC adapters clearly labeled. Do you have a different method for labeling your AC adapters? If so, we'd love to hear about it in the comments section.
Comments
Plastic post-it notes make great cable labels, especially for usb gauge cables. Just fold the label in half over the cable and write on the colored section.
i prefer to wrap my tape around the cord and stick it to itself. then i have a little flag to write on. but for the actual power converter, i think it looks more professional to use a metallic silver Sharpie pen. lots of rough handling can wear the ink off, but it's a breeze to touch up again.
and i knew a collegue that used clear shipping tape as a flag, but he put tiny cards in the flag. then he could write in a tracking number as well as what the cord attached to.