While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Advanced Energy (NASDAQ:AEIS) climbed 5% this morning after Needham upgraded the power conversion products company from hold to buy.

So what: Along with the upgrade, analyst Y. Edwin Mok planted a price target of $23 on the stock, representing about 18% worth of downside to Monday's close. While value investors might be turned off by Advanced Energy's run-up over the past year, Mok sees some decent room to run given the strong growth in both its thin film and solar inverter segments.

Now what: Needham expects Advanced Energy to post market-matching Q3 results with a good chance of upside Q4 guidance. "While we have been more cautious on AEIS's solar growth rate, we believe the business will grow in 2014 on an improved U.S. product portfolio and international expansion," noted Needham. "Our model suggests that the current stock price does not assign any value to the solar business." With a rock-solid balance sheet and forward P/E of 11, I'd have to agree that Advanced Energy's downside looks limited.