JBL Creature 2 Blowing Fuse?

I brought a JBL Creature 2 speaker system in black off ebay hoping it to be a simple fix. As soon as i hook the adaptor up to the main unit, the fuse in the adaptor blows the moment its turned on. When the transformer is off load I.E not connected to anything it has a steady voltage and the fuse if fine.
I tried to replace the fuse in the adaptor but it blows up every time.

The adaptor is an 18v 3.5A with a 5A 250V Fast blow fuse.