Hello (Sorry for being off topic)

I've recently recieved an old Macintosh Portable without the powersupply.
Therefor I need to know where to connect the plus and minus pole to the
computer. There is a sticker indicating DC 7.5V 2A but not which is plus
and minus.

I would deeply appreciate any help. I really want this 'super computer'
up and running.  :)

/Olof