Activist investor Paul Singer's Elliott Management on Monday revealed its latest target in the power and utilities space: Sempra Energy.

If that pairing sounds familiar, it should. Last August, Singer played a pivotal role in Sempra's purchase of Oncor, in the process, spoiling Warren Buffett's bid for the Texas utility. By threatening to launch a rival offer for Oncor, Elliott exploited the Oracle of Omaha's aversion to bidding wars and cleared a path for Sempra to acquire the Texas-based operator of transmission and distribution lines.

Now, Elliott and Bluescape Resources — frequent allies in activist campaigns in the utility space — are taking issue with Sempra's business mix less than a year after Singer helped add Oncor to its portfolio. The investors on Monday called for an overhaul of Sempra's board of directors and a strategic review of its assets and operations.

The firms say they can reverse a period of underperformance for the San Diego-based Fortune 500 company and unlock $11 billion to $16 billion of value, penciling out to a boost of $139-$158 per share for investors.

"Despite the attractive characteristics of its businesses, Sempra shares are deeply undervalued by the market. In our view, this persistent and substantial undervaluation stems from a focus on sheer size that has permeated management and Board thinking," Elliott portfolio manager Jeff Rosenbaum and Bluescape Executive Chairman C. John Wilder said in a letter to Sempra's board.