Exhibit 21

AMERICAN POWER CONVERSION CORPORATION  Subsidiaries as of December 31, 2003

|Subsidiary                                          |                                                   | Place of
Incorporation                                                    
|--------------------------------------------------- | ------------------------------------------------- | --------------------------------------------------------------------------
|APC America, Inc.                                   |                                                   | Delaware                                                                  
|APC Sales & Service Corp.                           |                                                   | Delaware                                                                  
|American Power Conversion Holdings Inc.             |                                                   | Delaware                                                                  
|Systems Enhancement Corporation                     |                                                   | Missouri                                                                  
|A.B.L. Electronics Corporation                      |                                                   | Delaware                                                                  
|APC DC Network Solutions Inc.                       |                                                   | Ohio                                                                      
|American Power Conversion Europe S.A.R.L.           |                                                   | France                                                                    
|American Power Conversion Corporation (A.P.C.) B.V. |                                                   | The Netherlands                                                           
|                                                    | APC Distribution Limited                          |                                                                           
|                                                    | APC (EMEA) Limited                                |                                                                           
|                                                    | APC Holdings B.V.                                 |                                                                           
|                                                    |                                                   | APC Deutschland GmbH                                                      
|                                                    |                                                   | American Power Conversion UK Ltd.                                         
|                                                    |                                                   | American Power Conversion Sweden AB                                       
|                                                    |                                                   | APC Benelux B.V.                                                          
|                                                    |                                                   | APC Australia Pty Limited                                                 
|                                                    |                                                   | American Power Conversion Portugal, Ltda.                                 
|                                                    |                                                   | American Power Conversion Spain S.L.                                      
|                                                    |                                                   | American Power Conversion Italia S.R.L.                                   
|                                                    |                                                   | American Power Conversion France SARL                                     
|                                                    |                                                   | APC Korea Corporation                                                     
|                                                    |                                                   | American Power Conversion Hong Kong Limited                               
|                                                    | American Power Conversion (Phils.), Inc.          |                                                                           
|                                                    |                                                   | American Power Conversion Land Holdings Inc.
(40%; 60% Filipino nationals)
|                                                    | APC (Suzhou) Uninterrupted Power Supply Co., Ltd. |                                                                           
|                                                    | American Power Conversion Singapore Pte Ltd.      |                                                                           
|                                                    | APC International Trade (Shanghai) Co. Ltd.       |                                                                           
|                                                    | American Power Conversion Poland Sp. z.o.o.       |                                                                           
|American Power Conversion Denmark ApS               |                                                   | Denmark                                                                   
|                                                    | Gutor Electronic GmbH                             |                                                                           
|                                                    | American Power Conversion Dublin Limited          |                                                                           
|                                                    | Silcon (Quingdao) Power Electronics Co. Ltd.      |                                                                           
|                                                    | Gutor Electronic Asia Pacific Sdn Bhd             |                                                                           
|American Power Conversion Mexico, S.A. de C.V.      |                                                   | Mexico                                                                    
|American Power Conversion Uruguay S.A.              |                                                   | Uruguay                                                                   
|APC Japan, Inc.                                     |                                                   | Japan                                                                     
|American Power Conversion (India) Private Limited   |                                                   | India                                                                     
|American Power Conversion Brasil Ltda.              |                                                   | Brazil                                                                    
|American Power Conversion Holdings (UK) Limited     |                                                   | United Kingdom                                                            
|                                                    | APC DC Network Solutions UK Limited               |                                                                           

74

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