Realise this is an old thread but I've googled my problem and found your same prob. It's a cctv system using hard drive for recording. It doesn't detect the hard drive and I see that the 12v connector is only getting 10v. The 5v is fine. I know this is the cause of the problem as if I give it 12v from an external supply it works fine.
Did you get a solution / workaround for your problem?