I think I remember having heard that "Jerry-built" originated in WW2. Jerry, of course was (reasonably affectionate) British slang for German (the non-affectionate equivalent being Hun). Anxious British householders, wishing to tell whether an approaching bomber was "ours" or "theirs" would tell the difference from the engine-note: the Jerry bomber (having been built by a nation not renowned for its engineering skill - that's meant to be a joke, Wolfgang) would not be able to synchronise its engines' speeds exactly, so the several engine-notes would "beat", giving rise to a characteristic mmmMMMmmmmmmMMMmmmmmmMMMmmm drone. The English bombers' engines, of course, were perfectly synchronised. And, I think, if you believe that, you'll believe anything.