1. For use in a semiconductor test system comprising a probe card and a supplemental current source, a method for reducing variation in a voltage supplied to a power input terminal of a semiconductor device under test, said method comprising: providing power through said probe card to said power input terminal of said semiconductor device under test; providing an input signal to said supplemental current source, said input signal corresponding to a temporary change in current drawn by said input terminal of said semiconductor device; and providing supplemental current to said input terminal from said supplemental current source in response to said input signal.