There really isn't an Adwords Certification, at least not through Google. There is the Google Advertising Professionals (GAP) account which allows SEM's to centralize and manage multiple client accounts which I am a part of. It, for the most part, is a great way for me to track all of my clients adwords accounts from a single logon.
Googles adwords training pages
http://www.google.com/adwords/learningcenter/
I've only found 3rd party certification which I would put in the same box as SEO certification programs. Pretty much subject to how good the program sponsors are, overpriced and at the mercy of "Are they really able to train you, and does it matter" syndrome.
Experience comes through trial and error and mistakes/success create experience.
Cheers
GAP
https://adwords.google.com/select/ProfessionalWelcome
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