Blix may have nailed it, depending on how old. Look at the label on the bottom; if it says "ACA Adapter," it's a 12 volter. "PSA Adapter" means it'll use any modern, normal 9v adapter.
If you have the older type, you can share power via a daisy chain (9V) with a non ACA pedal (any brand, doesn't have to be Boss) and it'll work fine. The other option is to mod it for 9V operation; a diode & a resistor are removed, with jumper wires replacing them. An easy mod.