well like pio said, it supposed to give same damage type as the main damage but half.
However on the DPS meter for some reason it showed that all my skills are dealing secondary damage as physical. I was doing damage on a summy, then I was shock of this fact, and I asked people in world chat. then I tested without any DA on a paladin and there was no physical damage added, I put DA again and test on the same pally surprisingly, there was no physical damage dealt. So I'm guessing it was some sort of bug that got fixed after me re-logging.