Barrel plug "standard" size?

I'm adding a DC power supply plug to a DAC I'm making. Which size is the most common?

I've seen Outer Diameter = 5.5mm and Pin Diameter = 2.1 - 2.5mm. My Graham Slee Ultra Linear PSU seems to be using 5.5mm and 2.5mm, but I have heard of other sizes being common, too.

Thanks,
Børge
 
I'll only be making one end of the cable. Others will be free to fit whatever PSU they have lying around. Therefore I'd like to make it maximally compatible. I'll start out with the one that fits my Graham Slee power here and let others swap out the receptacle if they have to