I only bought one and that was quite recently for general handheld device charging purposes here. I bought it because the wireless charging pad I bought didn't come with one...
Beyond that, all the ones I own came with pedals or the devices that need them. I guess I don't technically need the ones I have for my pedals, as I'm using universal power supplies of course, but I guess if I ever wanna give a pedal away, or sell one, I can give them the pedal, the box, the manual, and the wall wart. That should be worth something.