Is there a way to repair my ac adapter?

Input is 120v, Output is 9v. Someone was running across the room and snapped the cord in half. I could probably strip the plastic insulation and twist the wires back together. It snapped close to where the "black box" is. The black box part plugs directly into the wall. I was trying to strip the plastic part off, when I saw a spark when I exposed the wires. So I'm assuming there is still a charge inside the "black box". So, I left it alone. Is this not a safe thing to do? Should I assume there is still a lot of electricity inside of it? This is an AC adapter for a keyboard.