You're describing one of the most delightful and fascinating activities of toddlerhood! Okay, maybe it's not so delightful if he sends a Tiffany lamp crashing to the floor but let's look at things from your son's perspective for a moment.
Toddlers spend a lot of time trying to understand how the world works. There's no malice in your son's behavior; he doesn't "know the act is wrong." Rather, it's a sign of his intelligence and curiosity. He's behaving like a scientist trying to figure out whether something is consistent and predictable.
The next time he approaches something and says to himself "No," join in. Say something like "That's right! No!" Then distract him with something else to do.
Finally, I'm concerned that your son is pulling on electrical cords. This would be a good time to go through your home again and "toddler-proof" it to keep him safe.
