The voltage is the same, but there is something different between the OBS and the SD IDM's. Us OBS guys swap up to a SD IDM and it smooths out the idle some, and gives a tiny amount of better throttle response.
That is correct they are not all the same voltage. Depending on the year of the IDM will be either 100v, 110v, or Then you have aftermarket upgrades ones with the resistor that takes them to 140v.