A power system with a power apparatus for an X-ray tube is disclosed. The power system includes an X-ray tube and a power apparatus for the X-ray tube. The X-ray tube has a cathode and an anode. The power apparatus includes a first power conversion unit, a second power conversion unit, and a power switch unit. The first power conversion unit produces a positive voltage and a driving voltage and the second conversion unit produces a negative. When the power switch unit is turned off by the driving voltage, the power apparatus outputs the negative voltage to suppress electron flow energy generated from the cathode of the X-ray tube, whereas the power apparatus outputs the positive voltage to provide electron flow energy to the anode of the X-ray tube when the power switch unit is turned on by the driving voltage, thus producing X-ray.