The Einhorn effect appears to be alive and well.
Shares of SunEdison and Conn's jumped Tuesday on news that David Einhorn's Greenlight Capital had opened new positions in them, continuing the tradition of traders acting in agreement with the hedge fund manager.
SunEdison rose from $18.79 a share just before news broke to close at just above $20, up 11.8 percent for the day. Conn's was trading at $43.82 until shortly before 2 p.m.; that shot up to about $48 before settling at $46.98 at market close, up 7.65 percent on the day. Sun rose marginally in Wednesday trading, while Conn's gave back some of its gains.
Those moves echoed the sharp movements Einhorn has caused in the past. In May 2012, for example, shares of Herbalife fell about 20 percent after Einhorn asked questions during a company call. In December 2010, Einhorn said on CNBC that he had bought a stake in Sprint Nextel; shares jumped more than 6 percent that day.
Greenlight disclosed the new SunEdison and Conn's positions in a letter to investors, which it used to make its bullish case.
"The declining cost of solar energy combined with the rising cost of conventionally produced electricity should position SUNE as a winner," the Greenlight letter said. "The company has built a large pipeline of attractive projects secured by credit-worthy buyers of electricity."
Greenlight valued SunEdison at about $35 a share assuming an initial public offering of its semiconductor business and a "modest" reduction of corporate debt. The hedge fund entered the trade at $15.55, according to the letter.
On Conn's, Greenlight said the retailer was also undervalued.
"We believe that this is a retailer with 15-20% unit growth and current double digit comparable store sales growth, and that the market overreacted to the moderately bad news (on credit losses)," the letter said. Greenlight got into Conn's at about $35.49 a share.
A spokesman for Greenlight declined to comment.
The firm manages more than $10 billion. Greenlight's main fund fell 1.5 percent in the first quarter, according to the letter. The largest winner was a long bet on Micron Technology. Green Mountain Coffee Roasters, a short, was the most significant loser.
—By CNBC's Lawrence Delevingne.