QuickLinks -- Click here to rapidly navigate through this document

Exhibit 21

Power-One, Inc.—List of Subsidiaries

NAMED ENTITY	JURISDICTION/COUNTRY
• Power-One Energy Solutions Pty. Ltd		Australia
• Power-One Renewable Energy Solutions Canada, Inc.		Canada
• Power-One Co. Ltd.		China
• Power-One Asia Pacific Electronics (Shenzhen) Co. Ltd.		China
• Power-One Renewable Energy (China) Co. Ltd.		China
• Power-One I/S		Denmark
• Power-One Denmark ApS		Denmark
• Power-One S.A.S.		France
• Power-One GmbH		Germany
• Power-One Renewable Energy Solutions Greece S.A.		Greece
• Power-One Ltd.		Hong Kong
• Power-One Renewable Energy Solutions India Private Ltd.		India
• Power-One Ireland Ltd.		Ireland
• Power-One Renewable Energy Solutions Israel Ltd.		Israel
• Power-One Italy S.p.A.		Italy
• Power-One Renewable Energy Solutions Japan K.K.		Japan
• Power-One Energy Solutions Sdn Bhd		Malaysia
• Power-One BV.		Netherlands
• Power-One Renewable Energy International BV		Netherlands
• Power-One AS		Norway
• Power-One Limited Liability Company		Russia
• Power-One Pte. Ltd.		Singapore
• Power-One s.r.o.		Slovakia
• Power-One Renewable Energy Solutions Spain S. L.		Spain
• Power-One AG		Switzerland
• Power-One Limited		United Kingdom
• P-O Nevada Corp.		USA
• PAI Capital LLC		USA
• Power-One Renewable Energy Solutions LLC.		USA
• Power-One Renewable Energy Solutions Asia Pacific LLC		USA

QuickLinks

Exhibit 21

Power-One, Inc.—List of Subsidiaries