Originally a Harrison product. The front panel on earlier HP versions is marked “Harrison 6516A DC Power Supply” next to the HP logo badge. Later production drops the word “Harrison”.
Front panel includes an analog meter covering 0-3.5kV, four thumbwheel switches to set the voltage, “+” and “-” output connectors, and a push-on/push-off lighted power switch. The right-most thumbwheel is actually a potentiometer, allowing the voltage to be set to a fraction of a volt.
Pictured below is a Harrison-marked example. The connectors shown are not original.