ITEM 1

1. Name of Issuer:
   Power-One, Inc.
   
   
2. Address of Issuer's Principal Executive Offices:
   740 Calle Plano, Camarillo, California 93012

ITEM 2

1. Name of Person Filing:
   Security Management Company, LLC
   
   
2. Address of Principal Business Office or, if none, Residence:
   One Security Benefit Place, Topeka, Kansas 66636-0001
   
   
3. Citizenship:
   Security Management Company, LLC is a Kansas limited liability company.
   
   
4. Title of Class of Securities:
   Common Stock
   
   
5. CUSIP Number:
   739308104

ITEM 3   If this statement is filed pursuant to Rule 13d-1(b), or 13d-2(b), check whether the
              person filing is a:

1. [  ]  Broker or Dealer registered under Section 15 of the Act (15 U.S.C. 78o).
2. [  ]  Bank as defined in Section 3(a)(6) of the Act (15 U.S.C. 78c).
3. [  ]  Insurance Company as defined in Section 3(a)(19) of the Act (15 U.S.C. 78c).
4. [  ]  Investment Company registered under Section 8 of the Investment Company Act of 1940
         (15 U.S.C. 80a-8).
5. [X]  An Investment Adviser in accordance with § 240.13d-1(b)(1)(ii)(E)
6. [  ]  An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F).
7. [  ]  A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G).
8. [  ]  A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act
          (12 U.S.C. 1813).
9. [  ]  A church plan that is excluded from the definition of an investment company under Section 3(c)(14)
         of the Investment Company Act of 1940 (15 U.S.C. 80a-3).
10. [  ]  Group, in accordance with § 240.13d-1(b)(1)(ii)(J).

ITEM 4   Ownership.

Provide the following information regarding the aggregate number and percentage of the class of securities of the issuer identified in Item 1.

1. Amount beneficially owned:
   As of December 31, 2005, Security Management Company, LLC has the sole power to direct the vote and to dispose of 6,413,900 shares of Power-One, Inc. common stock of a total of 85,197,000 shares outstanding.**
   
   
2. Percent of class:
   7.53% of the common stock
   
   
3. Number of shares as to which such person has:
   (i)    Sole power to vote or direct the vote:   See Item 4(a) above.                        6,413,900 shares of common stock
   (ii)   Shared power to vote or direct the vote:                                                     Not applicable
   (iii)  Sole power to dispose or direct the disposition of:   See Item 4(a) above.      6,413,900 shares of common stock
   (iv)  Shared power to dispose or direct the disposition of:                                   Not applicable

**This report is being filed on behalf of Security Management Company, LLC ("SMC"), a Kansas limited liability company, and/or certain investment advisory clients relating to their collective beneficial ownership of shares of common stock of the Issuer. SMC is a registered investment adviser under Section 203 of the Investment Advisers Act of 1940. As a result of its role as investment adviser, SMC may be deemed to be the beneficial owner of the securities of the Issuer for purposes of §13(d) and 13(g) of the Securities Exchange Act of 1934. SMC has the sole power to dispose of the shares.

ITEM 5   Ownership of Five Percent or Less of a Class.

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following [  ].

ITEM 6   Ownership of More Than Five Percent On Behalf of Another Person.

Certain advisory clients of Security Management Company, LLC have the right to receive or the power to direct the receipt of dividends from or the profits from the sale of such securities.

ITEM 7   Identification and Clarification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.

Not applicable.

ITEM 8   Identification and Clarification of Member of the Group.

Not applicable.

ITEM 9   Notice of Dissolution of Group.

Not applicable.

ITEM 10   Certification.

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.