Though the stock market offers few certainties, one fact you can take to the bank is that dividend-paying stocks have vastly outperformed nondividend-paying companies over the long run. That's because dividend stocks are typically profitable and have time-tested business models, making them the perfect dangling carrot for long-term income-seeking investors.

However, as you're probably aware, no two dividend stocks are alike. Among the hundreds upon hundreds of dividend stocks for investors to choose from is a group of a few dozen elite income stocks known as "Dividend Aristocrats." A Dividend Aristocrat is a dividend stock that's increased its aggregate annual payout for at least 25 consecutive years. Presumably, a company needs to be highly profitable and have excellent long-term visibility to amass such a streak.

But even within this small grouping of Dividend Aristocrats lies another, even rarer subset of dividend-paying companies. I'm talking about a group of Aristocrats paying out a high-yield dividend -- i.e., one that works out to 4% annually or higher. If you're looking to add rock-solid income stocks to your portfolio that have time-tested business models and a track record of success, then here are three stocks to consider buying.

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AT&T

Telecom and content service provider AT&T (T 1.07%) has long since put to bed its high-growth days. After raising its dividend for the 35th consecutive year in December, though, it's also pretty apparent that AT&T's business model is about as rock-solid as they get

Although it's grown slowly in recent years, AT&T's wireless segment looks to be on the verge of an uptick in demand. The ongoing rollout of 5G networks should provide coverage throughout most of the country by next year, which is when we'll really see 5G-capable smartphones hitting stores. It's been a while since a smartphone replacement cycle really injected some excitement into the U.S. wireless market, but we look to be on the cusp of having that happen. Since wireless data is a high margin component for AT&T, it should benefit handsomely from its investments in this new high-speed network.

AT&T's video and television platform also shows promise, even if its near-term results don't suggest that. The acquisition of Time Warner and its prized assets -- the CNN, TNT, and TBS networks -- were supposed to act as dangling carrots that draw viewers to AT&T's streaming and television platforms. However, net customer losses have increased in the past two quarters. The reason this isn't too much of a concern, as noted by management, is that these losses are customers who are primarily on promotional contracts. These aren't particularly profitable for AT&T, which is why their loss has actually led to steadily higher average revenue per user in this segment. AT&T is choosing quality over quantity, and that's great news for its margins. 

If you want an income stock whose 6% dividend yield absolutely trounces the U.S. inflation rate, AT&T is your stock.

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Cardinal Health

On the surface, drug distributor and medical device company Cardinal Health (CAH 0.57%) may not look like much. It's currently operating in two avenues of healthcare that have been, without mincing words, terrible of late. Medical device commoditization has threatened pricing and margins, while pharmaceutical pricing has faced backlash in the U.S., spilling over from brand-name drugs to generics. This has combined to weigh down Cardinal Health's share price and pump up its yield to 4.1%.

However, Cardinal Health hasn't raised its dividend for 34 consecutive years because it's been lucky. Rather, it's because the company knows how to navigate the sometimes tricky healthcare landscape, and is also perfectly positioned to take advantage of one big trend: increased longevity.

It's no secret that life expectancies in the U.S. have risen over many decades, and more people are living into their 60s, 70s, or longer, than ever before. But as people live longer, their need for maintenance medicines and medical devices rises. We're just on the cusp of this shift, with baby boomers beginning to leave the labor force. Over time, boomers are expected to provide a healthcare boom of their own. With Cardinal Health supplying generic drugs and various medical products and devices to hospitals, it's perfectly positioned to benefit from an aging society that has improved access to medical care.

Plus, it's hard to overlook that Cardinal Health is valued at a historically low forward price-to-earnings ratio of just 9. Even with the potential for near-term hiccups, the future looks bright for Cardinal Health.

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Chevron

The final high-yield Dividend Aristocrat to consider buying right now is integrated oil and gas giant Chevron (CVX 0.40%). Despite crude being well off its highs, Chevron is still paying out 4% annually, and has increased its stipend to shareholders for an impressive 32 consecutive years.

One reason Chevron has been able to stay so consistent on the dividend front -- even though crude prices have been anything but consistent over the past decade -- is the company's ongoing investment efforts and its focus on boosting production. Upstream operations for Chevron (i.e., the drilling side of the business) continue to surprise to the upside, with production in the Permian Basin and Gulf of Mexico generally coming in ahead of expectations. To add, even if Chevron's core upstream business is struggling under the weight of lower crude prices, its diversified midstream (pipeline) and downstream (chemicals and refining) operations tend to step up to hedge this downside.

Unlike a number of its oil and gas peers, Chevron's balance sheet is also a source of strength. Sure, it may have $37.2 billion in total debt, but this is less than 24% of total equity, and just a little more than the nearly $31 billion in operating cash flow the company has generated over the trailing-12-month period. Debt isn't a big concern for Chevron, and it has little qualms about making big investments or acquisitions.

Chevron is also attractive on a value basis. At less than 1.5 times book value, Chevron is a lot closer to a 20-year low in this metric (just under one times book value) than its 20-year high of nearly four times book. Chevron's forward P/E ratio of less than 15 would also be a mark investors haven't seen in about four years.

All signs point to Chevron pumping up income investors' portfolios over the long run.