X0203 3 2011-04-29 0 0001137091 POWER SOLUTIONS INTERNATIONAL, INC. FMRT 0001044321 MARXE AUSTIN W & GREENHOUSE DAVID M C/O SPECIAL SITUATIONS FUNDS 527 MADISON AVENUE, SUITE 2600 NEW YORK NY 10022 0 0 1 0 Convertible Preferred Stock 0.375 Common Stock 2343526 I By Limited Partnerships Each share of Series A Convertible Preferred Stock is initially convertible at any time at the election of the holder This is a joint filing by Austin W. Marxe (Marxe) & David M. Greenhouse (Greenhouse). They share voting and investment control over all securities owned by Special Situations Fund III QP, L.P. (QP), Special Situations Cayman Fund, L.P. (Cay) and Special Situations Private Equity Fund, LP (PE), respectively. 4,900 PS cvrt into 1,640,468 shares of CS are held by QP, 1,400 P.S. cvrt into 468,705 shares of CS are held by Cay and 700 PS cvrt into 2,343,526 shares of CS are held by PE. The interest of Marxe and Greenhouse in the shares of Preferred Stock owned by QP, Cay & PE is limited to the extent of his pecuniary interest. The shares of common stock issuable upon conversion of the Series A Convertible Preferred Stock are subject to the limitations, set forth in the Certificate of Designation. Austin W. Marxe 2011-05-10 David M. Greenhouse 2011-05-10