They obviously didn't do the proper due diligence. They did what was legally required, but they did not do what was necessary to avoid to avoid the business nightmare they're in now.
Seriously, how novel is a USB power brick? It's not like the thing was designed from scratch for the first time for them... It looks identical to the one you get with iPhones/iPads.
I would have assumed, as they probably did, that it is a very plain vanilla component and not belabored it. The art of shipping is to know when to take certain risks related to he product.
Overthinking a mass-produced commodity power brick isn't a smart use of time.
