Need help identifying a mystery component with double-diode marking
I think you are on the right track, but the 12 in the part number is a red herring, IMO. Probably a date-code.  

After a bit of detective work, the most likely candidate I found was this ESAC63-004 common cathode Schottky diode array:




  


From what you say, it could be the rectifier of the output of the power supply, as can be seen in an image of a DELL power supply found here (emphasis on the image is mine):





EDIT

Another datasheet for the same part can be definitive (yellow highlighting is mine):


  


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