I've been working with electronic devices since the late 1980's. During all these years, and yes I still work with electronics, I've never come across a "bad new cap." Seriously. I've had caps go bad over time and blow because of reversed polarity. But I've not seen a bad one come off the assembly line. Statistically "bad caps" must exist. But I've never seen one first hand.

Human error is the culprit the vast majority of the time.