Tech stereo damaged by dimmer switch outlet, why?
It is not just a lower voltage what comes out of the dimmer. It was probably a phase control dimmer (as opposed to a reverse phase control dimmer) as they are cheaper and more common. This type of dimmer switches on in the middle of the AC cycle and switches off at the zero crossing and by this controls the average power that the device can take.


(red is the voltage after the dimmer)

The sudden rise of the voltage can be a problem for devices whose input is capacitive (behaves like a capacitor/has a capacitor parallel to its input) because a capacitor has a low resistance when it's empty and therefore takes a very large current when the dimmer suddenly switches on. It's possible that this just blew the fuse of your stereo.

Complex electronic devices in general shouldn't be dimmed, however more simpler switched power supplies (for lighting etc.) can sometimes be dimmed with a reverse phase control dimmer. That is one that switches on at the zero-crossing and then suddenly off in the middle of the cycle. On the other hand these dimmers cannot be used for devices with an inductive input because inductors (coils, e.g. a transformer) produce high voltages when suddenly switched off.