Cobras are in the genus Ophiophagus, Kingsnakes in the genus Lampropeltis. It's unclear to me whether data shows that members in the latter genus definitively suffer adverse consequences when members of the Order Serpentes are excluded from their dietary regimen.
Kingsnakes will eat almost anything living that fits in the tube, that much I know. I'd probably also criticize the owner of a Burmese Python for feeding it a small mixed-breed dog, but that also might be construed as being judgmental...