Psst... Do you want to know a secret? Warren Buffett has a portfolio of stocks that aren't included in Berkshire Hathaway's (BRK.A) (BRK.B 0.27%) regulatory filings.

I'm referring to stocks owned by New England Asset Management (NEAM). Although the firm is wholly owned by Berkshire, its holdings are revealed in separate regulatory filings to the Securities and Exchange Commission. 

While some of the stocks held by NEAM are also owned directly by Berkshire, many of them aren't. What are the three top stocks in Buffett's secret portfolio and should you buy them?

1. Wells Fargo

NEAM's biggest positions are in exchange-traded funds (ETFs). The top individual stock in its portfolio is Wells Fargo (WFC -0.37%) -- but with a catch.

Buffett's secret portfolio owns nearly 165,000 shares of Wells Fargo's common stock. However, it has an even more valuable position in the Series L convertible class A preferred stock. These shares pay an especially juicy dividend yield of 7.5%. 

Berkshire Hathaway was once a major shareholder of Wells Fargo. However, the big bank's missteps in past years caused Buffett to decide to throw in the towel on the stock. 

I think that Wells Fargo is now a good pick for investors, though. The stock has held up well with several U.S. banks failing earlier this year. Its valuation also looks attractive with shares trading at a forward earnings multiple below 9x.

2. Microsoft

Buffett has been a longtime admirer of Microsoft (MSFT 0.99%). He also continues to be a good friend of the tech giant's co-founder and former CEO, Bill Gates. But Microsoft wasn't included in Berkshire's portfolio.

It does make up more than 2% of NEAM's holdings, though. The Berkshire subsidiary owns roughly $18.3 million of Microsoft shares.

Microsoft has been a great stock to own in 2023. It's up over 40% thanks primarily to investors' excitement about the prospects of artificial intelligence (AI).

I wouldn't be surprised if the high-flying stock pulls back somewhat in the near future. However, Microsoft remains a great pick for long-term investors, in my view. It has excellent prospects in multiple hot technology areas, including cloud services, gaming, and AI.

3. JPMorgan Chase

Buffett's secret portfolio also features a sizable stake in another bank stock in addition to Wells Fargo. NEAM owns around $14.3 million of JPMorgan Chase (JPM 0.46%) shares.

As was the case with Wells Fargo, Berkshire Hathaway used to own shares of JPMorgan Chase. However, Buffett decided to completely exit Berkshire's position in the big bank in the fourth quarter of 2020 after selling a big block of shares earlier.

JPMorgan Chase ranks among the better-performing bank stocks so far this year. Because of its large size and rock-solid balance sheet, the stock is viewed by some investors as a safe haven.

I think that JPMorgan Chase is a good choice for long-term investors, especially those seeking income. Its dividend yield currently stands at nearly 2.8%. JPMorgan (and Wells Fargo) recently announced dividend increases after sailing through the Federal Reserve's stress test.

What about the biggest holding of all?

As previously mentioned, Buffett's secret portfolio actually owns larger positions in a few ETFs than it does in Wells Fargo, Microsoft, or JPMorgan Chase. NEAM's biggest holding of all is the SPDR S&P 500 ETF Trust (SPY 0.42%).

This index ETF makes up more than 13.7% of NEAM's portfolio right now. It's also a minor holding for Berkshire Hathaway. 

Is SPY a buy, too? My take is that its valuation is at a level where a pullback could be on the way. However, buying and holding the S&P 500 ETF is a good strategy over the long term.