A power supply for testing an integrated circuit includes a source voltage input terminal for receiving an input voltage. The power supply serves as both a DUT active power supply and an IDDQ measurement circuit, without the need for switching between separate DUT active power supply and IDDQ measurement circuits. In one embodiment, a current source output driver includes a diode across a current sensing resistor inside a feedback loop. This minimizes VDD changes when the DUT demands transient current, such as when loading IDDQ test vectors. Moreover, with decreased transient changes in VDD, dielectric absorption effects of a decoupling capacitor are reduced.