If 20V was fed into a camera expecting around 9V through a dummy battery setup, the most likely outcome is electrical damage. In the best case, a protective fuse or similar component failed first. In the worst case, other power circuitry was damaged as well.

There’s usually no meaningful home fix for this unless you have advanced electronics repair skills and board-level diagnostics. Most camera repair providers will diagnose the damaged section and, if possible, replace the affected board rather than repair individual parts.

So the practical next step is professional service, ideally through Sony or an authorized repair center. They can determine whether only one board was damaged or whether the repair cost is too high to justify.

For the future, use a properly regulated power source and coupler designed specifically for the camera to reduce the risk of over-voltage damage.