For an a200 you need to use a Sony A mount teleconverter. As mentioned, there are several brands available - Sony, Tamron, Sigma, Kenko to name a few.
The deciding factor is actually what lenses you want to pair it with.
The Sony (and Minolta / Konica-Minolta) branded teleconverters only work with G series lenses (with a couple of exceptions). The Sigma brand Teleconverters generally only work with Sigma lenses. Kenko teleconverters work with any A mount lens.
Personally I own a sony 1.4x TC and a kenko 2.0x TC - both are very good.
From one of your earlier posts I see you have a tamron 55-300. It might be worth noting that TCs generally perform best with prime lenses (eg fixed focal length lenses, such as a 300mm f2.
rather than superzooms - lenses with very large zoom ranges tend to have some compromises which TCs can acentuate... so you may want to try one in a camera store before commiting money to it