I like to use the cake extender recipe I got on this sight for all my cakes white included --- 1 cup sugar, 1cup flour, 1/3 tsp salt, 1 egg( for the white cake I use just the egg white) and 8 oz container yogurt(vanilla for white cake or complimentary flavor for other cakes).
My white cake stays nice and white and gives my cakes a firmer moist texture my clients love.
Here's the extended flavors version of the WASC cake recipe:
http://tinyurl.com/2cu8s4
(If using DH white cake mixes, the full WASC cake recipe will yield a tad over 14 cups of batter which is great for large pans or multiple smaller cakes.)
Adding pudding mix to the WASC (especially if using a cake mix that contains pudding) will significantly alter the recipe. 
A cake formula with excessive sugar will result in a cake layer that may fall upon cooling.*
Cake trouble shooting charts:
http://tinyurl.com/2p5bdu
http://tinyurl.com/32goqe
* It has been my experience that the cake layers can also be heavy and gummy.
HTH
I love the wasc recipe!! BUT I also have come to LOVE the Enhanced Cake Formula posted on cc. I used it for cupcakes Saturday using a DH white mix and I got mucho rave reviews at a church social. And coming from the older ladies, with lots of years of baking experience no doubt, in my new church I thought that was pretty special. Look it up. This recipe calls for 1 stick of butter, a cup of sour cream and three large eggs, in addition to the mix and additional sugar and flour. It makes a wonderfully delish white cake. Light in texture I'd say. It's sure worth a try. I iced the cuppies with Sharron (SS's) bc and the things practically melted in your mouth, to quote one little ole lady.
** The butter is optional, but highly recommended. Yum!!!!!
I also have to add that I'm darn glad those left over cuppies are gone, as of tonight.
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