It’s convenient that the 5.5/2.1 mm center-positive DC connector is nearly ubiquitous among DIY electronics. On the other hand, the “whoops I grabbed the wrong supply and killed my LED strip” tragedy is almost a weekly occurrence in the forums. I’ve done it too. They all look the same.
You don’t need a fancy labeler for this (but they’re fun!). Tape will do. Or bread clips. Whatever, avoid the Magic Blue Smoke Monster and label all your power supplies one way or another.