It should come with a few center negative cables. They are colour coded these days and the manual should explain which cable is what There's probably some sort of label or imprint on the cables itself as well. The downside is that you're not wireless anymore. It's also a bit overkill for just a B3 in my opinion. Might as well use the regular power supply unless you have more than just the B3 to power.
Something else to consider: The power connector on Zoom devices sits rather deep inside the casing. I have no idea if the cables from a 1-spot are deep enough for Zoom devices. They might (and probably are), but I never used a 1-spot myself. Test it before you buy. I did test the Ripcord and they fit even the newer Zoom pedals so it should work on the B3 as well.
On another note: Call me paranoid, but I don't like buying 2nd-hand power supplies. I don't know how they were used (or abused) and I have no idea when it's gonna die on me. I just like to have warranty on stuff like this. Like you, I don't like to cut corners on power supplies. The Thomann powerbank I mentioned above was an experiment that went a lot better than expected so I use that now, even though I still carry a backup power supply out of habit.
As with everything, YMMV.
