Power Adapter standards for DIYStompboxes

[peterv999]

Hi,
I'm wondering if someone could advise me in specifying  a 9Volts or a 12 volts  AC/DC power adaptor + PCB contra part that is regarded "standard" with respect to mechanical fit. I've looked around for standards but could not make any sense of it. Obviously the current requirements are there also but the emphasis is on the mechanical fit.

Regards

Piet

[R.G.]

2.1mm pin, 5.5mm barrel, center negative.

[StereoKills]

9v DC for *most* effects.