Another question has addressed how the Discord Orb and the Caduceus Damage Boost interact, but stacking is inconsistent in Overwatch. So far, it appears that unlike bonuses are multiplicative, while like bonuses are additive if they stack at all. But I'm unsure if that is truly the case across the board, and I'm also uncertain if that extends to elements which are not character abilities.
Can anyone help clear up how the 50% bonus from Discord and the 100% bonus from eligible headshots (150% for Widowmaker) stack? Is the total damage 250%, or 300%?