Those specs seem really old, and IMO not worth really spending money on. However if you must then I would stay away from the GT 710, if you must have a graphics card for soemt reason, you should get a GT 1030, its a much better card and in there not have an issue as the 1030 draws very low power, something around only 30 watts with a peak of around 50.
Again this is stretching the capability of your PSU, and I would recommend just building a new system