You know those little desk fans that come with a USB now and also an adapter to plug into the electrical outlet. I don't plug those into my laptops ever - who knows if there's a payload on them.
I will say this. I currently work, and have worked at, a few secret and top secret facilities - and the number of people I see plugging those (and similar) devices into their laptops is scary.
If such a device is able to cause a compromise / incident in a secure facility, well, several different "failures" at several different levels have occurred in order for it to get to that point.