May be wrong, but I don't think there is any such thing as an Apple 'certified' cable. They might be branded 'made for iPhone', but the manufacturer is simply self-certifying that he has joined the program and read all the documents.
Per Apple charging leads, there are I think two problems... First, some cables are 'chipped' and so bootleg clones simply won't work at all. Secondly, iPads will draw a hefty current (over 2A) from a charger that provides it. The voltage drop in the cable when such a high current flows can be significant and, just maybe, the terminal voltage at the device becomes insufficient?
I have tried various non Apple cables, not one of them worked reliably for iPad. Some refused to charge at all, others looked like they were charging, but weren't, or were charging so slowly that any actual use of the device during charging translated to net discharge.. That said, I've a couple of car IPhone chargers that seem to work ok with phones, but not tried them with iPads.