This manufacturer cited is one of several making a generic of Wellbutrin XL 300---but please make note of what I have placed in italics in the quote below:
Withdrawal of Generic Budeprion for NonbioequivalenceJanet Woodcock, M.D., Mansoor Khan, R.Ph., Ph.D., and Lawrence X. Yu, Ph.D.
December 5, 2012DOI: 10.1056/NEJMp1212969
Here is an excerpt of the professional article
published on December 5, 2012, at NEJM.org. (New England Journal of Medicine)
"...The Food and Drug Administration (FDA) has completed a head-to-head bioequivalence study of single doses of the generic drug Budeprion XL 300 mg (extended-release bupropion hydrochloride, manufactured by Impax Laboratories and distributed by Teva Pharmaceuticals) and the brand-name drug Wellbutrin XL 300 mg (Biovail). The agency has concluded that Budeprion XL 300 mg cannot be considered therapeutically equivalent to the brand-name product. We at the FDA are therefore changing our bioequivalence recommendations for extended-release bupropion products and have asked other manufacturers of 300-mg extended-release bupropion products to conduct additional bioequivalence studies." [italics mine]
http://www.nejm.org/doi/full/10.1056/NEJMp1212969?query=TOC
For anyone using the 300 mg dose, you might call your pharmacist who would be able to tell you what generic was dispensed to you.