UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q/A

(Amendment No. 1)

For the Quarterly Period Ended: June 30, 2011

OR

For the Transition Period From              to             

Commission File Number: 000-52213

Power Solutions International, Inc.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (630) 350-9400

Format, Inc.

3553 Camino Mira Costa, Suite E, San Clemente, California 92672

(Former name or former address, if changed since last report)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    Yes  x    No  ¨

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Website, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).     Yes  x    No  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See definitions of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act. (Check one):

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).     Yes  ¨     No  x

As of August 12, 2011, there were 10,770,083 outstanding shares of Common Stock, par value $0.001 per share, of the registrant.

EXPLANATORY NOTE

The purpose of this Amendment No. 1 on Form 10-Q/A to the Quarterly Report on Form 10-Q of Power Solutions International, Inc. (the “Company”) for the period ended June 30, 2011 (the “Form 10-Q”), as filed with the Securities and Exchange Commission (the “SEC”) on August 15, 2011, is solely to furnish the interactive data files on Exhibit 101 to the Form 10-Q within the 30 day grace period provided in accordance with Rule 405 of Regulation S-T. Exhibit 101 to this report furnishes the unaudited condensed consolidated financial statements and the related notes to the unaudited condensed consolidated financial statements formatted in Extensible Business Reporting Language (XBRL).

Users of this data are advised that pursuant to Rule 406T of Regulation S-T, the interactive data files on Exhibit 101 hereto are not deemed filed or part of a registration statement or prospectus for purposes of sections 11 or 12 of the Securities Act of 1933, as amended, are not deemed filed for purposes of section 18 of the Securities and Exchange Act of 1934, as amended, and are not otherwise subject to liability under such sections.

No other changes have been made to the Form 10-Q, apart from revisions to Item 6 made to (A) provide updated references to the most recent versions of exhibits that have been filed with the SEC and (B) clarify the filing dates of the reports where exhibits that are incorporated by reference to the Company’s Current Report on Form 8-K dated April 29, 2011 are located. This Amendment No. 1 on Form 10-Q/A speaks as of the original filing date of the Form 10-Q, does not reflect events that may have occurred subsequent to the original filing date, and (except as described above) does not modify or update in any way disclosures made in the Form 10-Q.

Item 6. Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.