I feel the traps get good work when I do deep dips and shrug hard as I go toward the bottom. This utilizes the traps to help stabilize the shoulders at this range of motion. Also they will be worked in handstand push ups, back levers, frog stands, elbow levers…basically you have to just shrug hard in any of these types of movements to utilize the traps.
For explosiveness in push ups do plyometric push ups.