The vitamin c i'm using from trader joes only has ascobic acid listed as an ingredient. Not sure how great the quality is. (can someone recommend a good quality. I was looking at the vitamin c foundation brand.)
Ascorbic acid is ascorbic acid. They are all formed from sugars, and all of these synthetics are extremely unstable. There are only a couple of manufacturers and these are sold to raw material suppliers who then private label the same exact product. So there is basically no difference between brands. The only differences would be added bioflavonoids, or buffering to make different ascorbates.
The best C is from natural sources, which are not only stronger, but also more stable. The best foods sources are watercress, kiwis, papaya, and berries. he best herbal sources are amla berry, acerola cherry and sea buckthorn.