The utility model relates to a jack which is formed by the combination of an existing lever type rack bar jack, a hydraulic buffer, a slider, and an upper and a lower two pairs of adjustable ejector pins. A plunger (piston) in the buffer is formed by the extension of the lower end of the rack bar, a lifting pawl and a check pawl are installed in the slider which can vertically move up and down along the base, the slider is supported on the two pairs of adjustable ejector pins, one ends of the two ejector pins are mutually hinged, the rest two ends are hinged on the slider and the base respectively, and the slider can be moved up and down by changing the intersection angle of the ejector pins. The utility model can be used as a power device for various manual operated carrying (scraping) trolleys, and has the advantages of long service life and convenient operation.