Why do some people add 1 tsp. of baking powder and 1 c. flour to their store bought cakes mixes? Does it give you more cupcakes, does it taste better? Do you add to all cake mixes even the ones with pudding? I just wanted to see if I was missing something.

Thanks so much

It's frequently called an "extender." But flour and baking powder aren't the only things that are added. You also need to add extra fat/oil and/or egg and sometimes sugar.

Yes, it does make more cupcakes than a regular box mix. As you experiment a little with different additional ingredients and flavorings, you'll find that your cakes can taste better than "plain" box mixes.

There's a fun book called "The Cake Mix Doctor" that will give you lots of ideas of different things you can add to ordinary cake mixes.

You also might want to search the recipe section on CC for "doctored" cake recipes.