Power connector size for GS108 switch

Due to space constraints, I need to use a 90 degree adapter to connect the power to the new GS108 I just bought.  The easiest solution is to get something like this adapter but I'm not sure the exact size.  I've measured the outside diameter of the power plug, it's 5.5mm, so it's almost certainly either 5.5mmx2.1mm or 5.5mmx2.5mm.  However I'd like to know for certain which one before I try and order something.