It appears to be for the Commodore Plus/4. I'll post links with pictures.

http://www.obsoletecomputermuseum.org/plus4/
http://www.obsoletecomputermuseum.org/plus4/plus4_2.jpg

Several Commodore computers had different revisions with changes to the power connector made, I guess this is one of them. The Vic 20 is another one.

http://www.classiccmp.org/dunfield/v...newwindow=true
http://www.classiccmp.org/dunfield/vic20/h/rside.jpg