If a client gives out requirements in dribs and drabs, the court agrees that the contractor isn't allowed to raise the price as a result.
When someone is starting to design a new product, they seldom come up with the entire thing in one hit. Features are added or removed.
For millenia we had a stick and a bit of string/cord for a drill. Then someone invented the drill bit and the brace. Later electricity came along and we got drill presses, and some years later we got drills small enough to be carried around. Then we got a variety of cordless drills till we reached what we have today - cheap battery-powered drills that can do a hell of a lot of work while being cheap enough even I have several of them and often use 3 separate ones for a job (one for the screw hole, one for the screw, and one for the larger hole in the held bit of wood - if I wasn't so lazy and using self-countersinking screws I'd have another for the countersink bit). We also have hammer drills, clutch drills, and where years back you needed a large compressor and a humongous bank-balance for the actual unit, we have cordless rattle-guns around the same size as a common drill, and for around the same price.
I and anyone else who has done any actual design work knows that there will be changes between the initial idea and the final result. Sometimes it'll be the wife suggesting the buttons would be more comfortable if moved along a bit, sometimes it's someone asking for a speed regulator, sometimes you yourself realise it'd be cool if it could also....
So when you do design work for others, you charge a set rate and drop the prices a reasonable amount for doing less work, or add to it a reasonable amount for doing more work.
$800 for a $1 USB charger is very very far from reasonable, and the criminal deserves to be charged and tried. If he'd not charged such an outrageous amount for the job he wouldn't be in the boat he is in now, even if he was operating outside the law. Hell, in this day and age it's such an obvious accessory he could've spent 20 seconds adding it to the design just in case, or as an added feature to even more please the customer.
What he hell is in his USB charger that's worth even $50 let alone $800? And what's in his battery/switch/pump/spray nozzle design that makes it worth $40, let along $4,000?