I thought that I had sorted through all of my old Apple adapters a while back, but today I came across another box of unlabeled white adapters. It's daunting to figure out what goes to what and which ones can be tossed out.
Thankfully, the last time I tackled this process I found and bookmarked this handy guide by Apple (complete with photos): About Apple video adapters and cables
By the way, to combat this problem I've started to do two things. First, for adapters that I occasionally use and that came in Apple's retail packaging, I place them back in the package after each use.
For all other adapters, cords, chargers, and such, I've been better about labeling them. I've tried various types of cable labels, but I'm finding that 3M painter's tape is a good and inexpensive solution. And, unlike some labels, it stays put yet comes off easily. For a similar yet prettier solution, I hear Washi tape works similarly well.
Hopefully, someday, technology and the industry will coalesce around one standard that can work for everything. Until then, I'm off to figure out what this is ... and to properly label it this time.