ebay purchase, should I leave bad feedback?

You don't get 10,000+ feedback by being a scammer. He's not the best seller, but not the worst by far. Have you contacted him about it at all? I'd say contact him, and if you don't hear back in a couple of days, leave the feedback. But if you just sit there, waiting for the cord and he doesn't know there's an issue, he can't fix it.