All my DC / DC converter have no housing. I can see the electronics. Most have a LM2596S from Texas Instruments. But there are certainly fakes ...
All I can say it to test carefully before attaching to your expensive camera.
Your LM2596S chips could be fake (google for
fake electronic chips) or more likely "off spec" units that failed quality testing but still appear to work at room temperature and lower current draws.
Also, cheap electrolytic capacitors are common. They don't actually meet the specs of the good ones but they appear to work - at least for a while.