These two companies can add huge upside potential to your portfolio.Want to instantly add huge upside potential to your portfolio? Check out fintech stocks. These companies are like banks but with the rapid growth rates of tech start-ups. Right now, two fintech stocks, in particular, look very attractive.Follow Buffett into this quality company trading at a discountIt pays to look at Warren Buffett's portfolio. For more than a decade, he's held onto one of the most successful fintech stocks in recent memory ...