The unit that will be investigated and described herein is what is called an electric fence charger. It is the unit that generates the high voltage used to drive an electric fence for containing pets or livestock.
Personally, I find anything that generates high voltage is inherently interesting. This applies to all high voltage items in general, be they Tesla coils, stun guns, automobile ignition systems, or whatever. Hopefully you will find this investigation interesting and educational.
Of couse, since this also means that a safety disclaimer is in order:
The device described here is powered by 120 VAC. Excercise caution when working with 120 VAC, as contact with it can be lethal! Unplug any 120 VAC device from power when investigating it!
The output side of this device is used to drive an electric fence, and can generate kilovolt pulses causing pain when contacted!
Exercise extreme caution when working with any high voltage device or 120 VAC powered device! Experiment at your own risk!