The dividend yield on the S&P 500 is very low these days. At 1.2%, it's near its lowest level in more than 20 years. Because of that, you won't generate much passive dividend income by investing in an S&P 500 index fund. While the S&P 500 doesn't pay much these days, plenty of other dividend stocks pay a lot more. One of the more impressive payouts comes from AGNC Investment (AGNC 0.52%), which currently yields almost 15%. Here's a look at how it can afford to pay such a lucrative dividend.A simple investme ...