He's wobbled Marquez, Pacquaio, Provodnikov and dropped some other sturdy fighters. He looks like he throws hard and you hear the impact, he's built like a tank... But never any KOs. It's hard to rate his power. Kind of like Ward's actually.
He also hit hard enough to drop the solid chinned Witter as Edner Cherry. Whatever his various opponent's various flaws might be, Bradley has faced a fairly relentless stream of very durable opponents dating back to Donald Camerena (Holt being the exception). If he had better timing he might accumulate more TKOs.