Standard unidirectional programmable DC power supplies are useful, flexible instruments that can find use in almost any electronics test application. The key word here, however, is almost. For a typical DC power supply, you program the output voltage and the supply maintains that specific voltage regardless of load variations (within the unit’s power and current-rating constraints) until you program another voltage. But for some applications, the stiff output characteristic of a standard supply due to high output capacitance and low source resistance is the opposite of what you need.