These supplies employ a unique variable output resistance so the voltage output can emulate a battery's response (U.S. Patent No. 6,204,647). They provide stable voltage outputs, even when a device-under-test (DUT) makes the rapid transition from the standby (low current) state to the RF transmission (high current) state. In addition, they can monitor DUT power consumption by measuring both DC currents and pulse load currents. The Keithley Model 2306's battery-simulator channel can be programmed to operate like a discharged rechargeable battery, sinking current from a separate charger or from the Model 2306's charger-simulator channel.