Do you think, generally speaking, when people take chargers that aren't theirs and don't return them when asked IN WRITING and given a chance to say they took them by accident, that they do it unintentionally? This happened to me twice in the last couple of weeks, once with someone in my family (as in, it could have been a niece, a nephew, or brother-in-law) and once with an acquaintance. I am tired of buying new chargers for my laptop.
This happens all the time. ALL THE TIME!!! Why does it make us so hulk-like? We spend a lot of time resenting chargers, when they take up prime real estate on the kitchen counter, or create a wire nest in the corner of our bachlorette's pad. I think if we looked at our charger as something we needed, we'd draw firmer boundaries when others want to borrow it. The insane way to do that is to overreact when someone wants to borrow it; the preferred way is to mark your charger as yours and something you can't easily replace.
Passively tell people to step away from your charger by creatively marking them as your own. Humans as animals respect unique visual markings since they show that this specimen is different than all the others, and that somebody loves it.
If I were to draw a line to represent the spectrum of Things Dear To My Heart, where one end is "LOVEIT", with a notch for a lover or whatever, and the other side "Shrug", with a notch for someone's sock that I found at the laundromat. My laptop, phone, and iPod (named nPod) are very close to the tip of the LOVEIT end, and usually, my charger is somewhere in the middle. But I used my handy-dandy label maker to slap my name right on my charger, and that pushed him closer to my Pepto-pink coffee maker notch on the LOVEIT end of the spectrum. As soon as you invest a few moments of your time to pass on your personality to an object, you're claiming it as belonging to the tribe of you. So if we expressed ourselves on our stuff with stickers or silly bands or paint blotches or the like, people wouldn't borrow them willy-nilly because, clearly, they're not as replaceable as we thought.
Your power source loves you, too, and I bet he wants a tattoo with your name on it. So tell everyone! And snap at them when they take your baby away from you.