Cook your pasta according to package directions and let it cool. Chop your veggies.
In a small bowl, make your dressing. Mix the mayonnaise, mustard, onion powder and white sugar and set it aside.
In a large bowl toss the pasta, capers, and veggies together until well-mixed, then toss with the dressing to coat everything completely.
Let the pasta salad chill for 1-2 hours prior to serving.