The voltage regulator in my generic reman alternator went bad twice. Both times voltage pegged to over 18 volts. My whinebro suddenly went nuts and hit a new high note, my headlights went HID and the interior lights all brightened up.

One thing I wonder about- is the battery also bad? It might just be starved for a charge because the alternator is failing. The battery should keep voltage up above 12 even if the alt shuts off unless it doesn't have a full charge on it.