Hi and welcome to JustAnswer,Thank you for the question and your patience. Should you still need assistance for information purposes only...Initially, is the Pioneer completely/electrically dead?
Yes; the voltage was almost doubled likely causing a fault in the power supply.
this would then be an internal hardware issue particularly. Are you then considering a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter and even a soldering iron?
A step-down transformer yes BUT only after it has been repaired.
Please post back how you would want to approach this and/or should additional information be needed.