As PsyDr said, VA typically gives a one step increase for board certification (although the decision ultimately depends on local leadership). Which if my math is correct, equates to about 3% and some change.
I've heard of other organizations providing 5% or 10% bumps, but don't have any specific AMC names for you.
Also, some random advice for VA psychologists: if possible, time your board certification so that it occurs soon after a step increase rather than just before one, as the bump can sometimes reset the clock for you next step increase. I wouldn't say it's worth putting it off multiple years, but if you're almost due for an increase, it might be worth picking a later oral exam date if possible.