Replacement wall charger question

I lost the wall charger for this air pump thing that I have. I want to buy a replacement charger, but I don’t know the exact specs. I’ll probably just get a universal charger, and looking at the writing on the pump it says 4.8V, but it doesn’t tell me if the pin is + or -. There isn’t that usual diagram thingy that you see on other electronics. Is there any way to figure it out? Is one config more common than others? What happens if I put the wrong tip on?

If you can find something else that you are convinced is ground, you could use a multi-meter to figure out which part of the plug is ground…

Or you could check the internet for the pump you have. The internet is **really **smart…

So is that open-end-plus [(-) --C-- (+)] or open-end-minus [(-) --Ↄ-- (+)]?

Heck, I’m not sure if open-end-minus is written (+) --C-- (-), since I haven’t seen it in so long. But you get what I’m asking right? Which part of the symbol refers to the ground?