If you're following the Motley Fool's rules for building a retirement nest egg, your portfolio's likely delivering respectable long-term growth. Still, you might be wondering how to spice up your performance without adding a great deal more risk.

Good news! It's possible to do just that. The key lies in how you add holdings with a bit more "oomph." Picking more high-risk individual stocks isn't the answer. Rather, tap into a specific approach, industry, or strategy with a diversified basket of stocks -- you'll know them better as exchange-traded funds, or ETFs. Here's a closer look at three such ETFs that could really supercharge your retirement savings.

iShares Exponential Technologies ETF

Let's face it: The technology sector has led the market for nearly 30 years now. That's because these companies are driving the most desired (and marketable) changes in the way we live our day-to-day lives.

Even so, not every tech stock is necessarily destined to be a market-beating leader. Ideally, there would be a way to limit your exposure to just the top names among technology stocks.

Well, the iShares Exponential Technologies ETF (XT -0.48%) is one such way.

The idea is simple enough. The iShares Exponential Technologies ETF "seeks to track the investment results of an index composed of developed and emerging market companies that create or use exponential technologies." In other words, the ETF -- which is based on the Morningstar Exponential Technologies Index -- holds "companies with significant exposure to exponential technologies, which displace older technologies, create new markets, and have the potential to create significantly positive economic benefits." Its holdings include many obvious picks like Nvidia and Microsoft. It also holds a number of compelling stocks that many retail investors might not find on their own, such as Palantir Technologies and Cloudflare.

And that's the real edge this fund has on other tech-related alternatives. Often, some of the best-performing stocks from a particular sector seemingly come from nowhere, as Nvidia did beginning back in 2016.

It's a relatively small fund, with only a little over $3 billion worth of assets in its pool. Don't let its size fool you, though. If you can stomach above-average volatility, this ETF's above-average performance during bull markets will be well worth it.

JPMorgan Equity Premium Income ETF

Buying growth stocks isn't the only way to beef up the growth of your retirement savings. You can do it with regular cash payments too, particularly when those payments dramatically exceed the sort of yields you might otherwise get from conventional dividend stocks or bonds.

Enter the JPMorgan Equity Premium Income ETF (JEPI -0.30%).

Just as the name suggests, this fund generates regular income that's passed along to its owners -- a lot of it. Its current annualized yield is right at 8.5%, which is well below its more typical rolling 12-month yield of 11%.

Too good to be true? With nothing more than a passing glance at the numbers, you might think that to be the case. Knowing the fund's managers' strategy, though, makes this strong yield make sense.

See, the JPMorgan Equity Premium Income ETF utilizes an options trading strategy known as covered calls. Whereas most speculators typically buy either call options (bullish) or put options (bearish), JPMorgan Equity Premium Income Fund's managers sell call options -- producing income as a result -- on the quality stocks the fund currently holds. While selling calls rarely produces huge one-off wins, the approach can be repeated over and over again for each stock in the portfolio. In fact, it likely will be repeated several times in a single year for most of the stocks in the portfolio.

The ironic downside is, such a strategy tends to work best in a flat-to-bearish market. When bull markets are lifting the values of all stocks, selling covered calls often means you'll end up being forced to sell the stocks you own.

That's not exactly the end of the world, though. After all, you're selling those stocks while (and because) they're on the way up, and they can always be replaced.

SPDR S&P MidCap 400 ETF Trust

Last but not least, while simple indexing makes the most sense for at least the majority of most investors' retirement portfolios, there's no law that says the S&P 500 (^GSPC -0.19%) has to be the only index you ever own a piece of. There's a case to be made for holding a piece of the S&P 400 Mid Cap index as well, via an exchange-traded fund like the SPDR S&P MidCap 400 ETF Trust (MDY -0.81%).

Large-cap companies sport market capitalizations of at least $10 billion. Small caps have valuations of between $300 million and $2 billion. There's a sweet spot in between them, however, that's often overlooked: the mid caps, with capitalizations of between $2 billion and $10 billion. It's a sweet spot simply because these companies have made it through the tough start-up stage and proved they have some staying power, but they're not yet big enough to have caught most retail investors' attention. They're also usually just starting to steal market share from their bigger competitors.

This index's long-term performance verifies the argument. Over the past 20 years, the S&P 400 has dramatically outperformed the S&P 500.

^MID Chart

^MID data by YCharts.

There were noteworthy short-term exceptions to this leadership. Take 2008's mortgage meltdown and the early 2020 correction that was set off by the start of the pandemic. All stocks tumbled during those periods, but mid caps in general fell more sharply than large caps. There were also a couple of periods when tech-led large caps charged ahead while mid caps were listless.

It's still ultimately worth the wild ride though. As the chart above also shows, mid caps typically bounce back and rally more strongly than their large-cap counterparts do.