Abstract: The present invention relates to a sag-swell generator for generating power signal with sag, swell and outage for use in testing custom power devices. The sag-swell generator comprises: a supply voltage unit for providing a supply voltage; a variable voltage adjusting unit for controlling the supply voltage according to a voltage ratio; a variable voltage-side switch unit selectively connected to the variable voltage adjusting unit; a transformer-side switch unit composed of dual switches connected anti-parallel to each other; and a transformer, a primary side of which being connected to the transformer-side switch unit and a secondary side of which being serially connected to a load and a (?) terminal of the supply voltage.