Ownership Submission
FORM 3
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
  Silver Lake Sumeru Fund LP
2. Date of Event Requiring Statement (Month/Day/Year)
05/08/2009
3. Issuer Name and Ticker or Trading Symbol
POWER ONE INC [PWER]
(Last)
(First)
(Middle)
2775 SAND HILL ROAD, SUITE 100
4. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
5. If Amendment, Date Original Filed(Month/Day/Year)
(Street)

MENLO PARK, CA 94025
6. Individual or Joint/Group Filing(Check Applicable Line)
___ Form filed by One Reporting Person
_X_ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Beneficially Owned
1.Title of Security
(Instr. 4)
2. Amount of Securities Beneficially Owned
(Instr. 4)
3. Ownership Form: Direct (D) or Indirect (I)
(Instr. 5)
4. Nature of Indirect Beneficial Ownership
(Instr. 5)

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly. SEC 1473 (7-02)
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB control number.

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 4)
2. Date Exercisable and Expiration Date
(Month/Day/Year)
3. Title and Amount of Securities Underlying Derivative Security
(Instr. 4)
4. Conversion or Exercise Price of Derivative Security 5. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 5)
6. Nature of Indirect Beneficial Ownership
(Instr. 5)
Date Exercisable Expiration Date Title Amount or Number of Shares
Series A Convertible Pref. Stock, par value $0.001 per share (1) (2) (3) 05/08/2009   (4) Common Stock, par value $0.001 per share 17,357,037 (5) (6) $ 1.35 (7) D (8)  
Series A Convertible Pref. Stock, par value $0.001 per share (1) (2) (3) 05/08/2009   (4) Common Stock, par value $0.001 per share 142,962 (5) (6) $ 1.35 (7) I See footnote (9)
6.0%/8.0%/10.0% Convertible Senior Notes due 2019 (1) (2) (3) 05/08/2009 05/08/2019(10) Common Stock, par value $0.001 per share 26,724,444 (11) $ 1.35 (12) D (8)  
6.0%/8.0%/10.0% Convertible Senior Notes due 2019 (1) (2) (3) 05/08/2009 05/08/2019(10) Common Stock, par value $0.001 per share 220,000 (11) $ 1.35 (12) I See footnote (9)
Warrant (right to buy Common Stock) (1) (2) (3) 08/08/2010(13) 05/08/2016 Common Stock, par value $0.001 per share 8,628,941 (14) $ 1.33 (15) D (8)  
Warrant (right to buy Common Stock) (1) (2) (3) 08/08/2010(13) 05/08/2016 Common Stock, par value $0.001 per share 71,059 (14) $ 1.33 (15) I See footnote (9)

Reporting Owners

Reporting Owner Name / Address Relationships
Director 10% Owner Officer Other
Silver Lake Sumeru Fund LP
2775 SAND HILL ROAD
SUITE 100
MENLO PARK, CA 94025
  X   X    
Silver Lake Technology Investors Sumeru, L.P.
2775 SAND HILL ROAD
SUITE 100
MENLO PARK, CA 94025
  X   X    
Silver Lake Technology Associates Sumeru, L.P.
2775 SAND HILL ROAD
SUITE 100
MENLO PARK, CA 94025
  X   X    
SLTA Sumeru (GP), L.L.C.
2775 SAND HILL ROAD
SUITE 100
MENLO PARK, CA 94025
  X   X    

Signatures

/s/ Ajay Shah, managing member of SLTA Sumeru (GP), L.L.C., general partner of Silver Lake Technology Associates Sumeru, L.P., general partner of Silver Lake Sumeru Fund, L.P. (see sign. of other Reporting Persons on the attached Exhibit 99.1) 05/15/2009
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 5(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) This Form 3 is filed on behalf of Silver Lake Sumeru Fund, L.P. ("SLSF"), Silver Lake Technology Investors Sumeru, L.P. ("SLTI"), Silver Lake Technology Associates Sumeru, L.P. ("SLT LP") and SLTA Sumeru (GP), L.L.C. ("SLTA"). SLT LP is the sole general partner of SLSF and SLTI. SLTA is the sole general partner of SLT LP. SLSF may be deemed to be a director by deputization of the Issuer.
(2) As the sole general partner of SLSF and SLTI, SLT LP may be deemed to be the indirect beneficial owner of the securities directly owned by SLSF and SLTI under Rule 16a-1(a)(2) promulgated under the Securities Exchange Act of 1934, as amended (the "Exchange Act"). However, pursuant to Rule 16a-1(a)(4) promulgated under the Exchange Act, SLT LP disclaims beneficial ownership of such securities, except to the extent of its pecuniary interest.
(3) As the sole general partner of SLT LP, SLTA may be deemed to be the indirect beneficial owner of such securities under Rule 16a-1(a)(2) promulgated under the Exchange Act. However, pursuant to Rule 16a-1(a)(4) promulgated under the Exchange Act, SLTA disclaims beneficial ownership of such securities, except to the extent of its pecuniary interest.
(4) The Series A Convertible Preferred Stock, par value $0.001 per share of Power-One, Inc. (the "Issuer") and initially priced at $1,000 per share (the "Series A Preferred Stock"), is redeemable at the Issuer's option after the fifth anniversary of the original issuance date. Subject to certain exceptions, the Series A Preferred Stock is redeemable at the option of the holders thereof on the fifth anniversary, and each successive anniversary thereafter, of the original issuance date. The Series A Preferred Stock is also subject to earlier redemption, repurchase or conversion in accordance with the terms thereof.
(5) This is the number of shares of common stock, par value $0.001 per share of the Issuer (the "Common Stock"), issuable upon conversion of the Series A Preferred Stock as of the date of this filing; however, conversion of the Series A Preferred Stock is prohibited if, following conversion, the holder, along with its affiliates, would (i) have voting power in excess of 19.9% of the Issuer or (ii) own in excess of 19.9% of the Issuer's outstanding Common Stock, except for any conversion in connection with and subject to the completion of (x) a public sale of the Common Stock issued upon such conversion, if following consummation of such public sale, such holder and its affiliates would not own more than 19.9% of the total shares of Common Stock then outstanding or (y) a third party tender offer for the Common Stock issuable thereupon.
(6) Under certain circumstances, shares of the Series A Preferred Stock may be convertible into shares of Series B Junior Participating Convertible Preferred Stock, par value $0.001 per share of the Issuer.
(7) Subject to anti-dilution adjustment pursuant to the terms of the Series A Preferred Stock.
(8) These securities are directly owned by SLSF. SLT LP and SLTA may be deemed to have indirect beneficial ownership of these securities. See Footnotes 2 and 3.
(9) These securities are directly owned by SLTI. SLT LP and SLTA may be deemed to have indirect beneficial ownership of these securities. See Footnotes 2 and 3.
(10) The Issuer's 6.0%/8.0%/10.0% Convertible Senior Notes due 2019 (the "Notes") mature on the tenth anniversary of the original issuance date. The Notes are also subject to earlier redemption, repurchase or mandatory conversion in accordance with the terms thereof.
(11) This is the number of shares of Common Stock issuable upon conversion of the Notes as of the date of this filing; however, conversion of the Notes is prohibited if, following conversion, the holder, along with its affiliates, would (i) have voting power in excess of 19.9% of the Issuer or (ii) own in excess of 19.9% of the Issuer's outstanding Common Stock, except for any conversion in connection with and subject to the completion of (x) a public sale of the Common Stock issued upon such conversion, if following consummation of such public sale, such holder and its affiliates would not own more than 19.9% of the total shares of Common Stock then outstanding or (y) a third party tender offer for the Common Stock issuable thereupon. Under certain circumstances, the Notes may be convertible into shares of Series C Junior Participating Convertible Preferred Stock, par value $0.001 per share of the Issuer.
(12) Subject to anti-dilution adjustment pursuant to the terms of the Notes.
(13) The warrant for the purchase of shares of Common Stock (the "Warrant") may be exercised prior to August 8, 2010 upon the occurrence of a fundamental change in the Issuer pursuant to the terms thereof.
(14) This is the number of shares of Common Stock issuable upon the exercise of the Warrant as of the date of this filing; however, exercise of the Warrant is prohibited if, following exercise, the holder, along with its affiliates, would (i) have voting power in excess of 19.9% of the Issuer or (ii) own in excess of 19.9% of the Issuer's outstanding Common Stock, except for any exercise in connection with and subject to the completion of (x) a public sale of the Common Stock issued upon such exercise, if following consummation of such public sale, such holder and its affiliates would not own more than 19.9% of the total shares of Common Stock then outstanding or (y) a third party tender offer for the Common Stock issuable thereupon.
(15) Subject to anti-dilution adjustment pursuant to the terms of the Warrant.

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