The GTX 750ti will draw 20A from the 12v rails. Your power supply allows for 22A from both of your 12v rails, which is sufficient if the psu actually delivers that power. The problem is that the GTX 700 series are known to draw more power than what is listed due to the GPUBOOST2.0 feature, which allows the GPU to continually draw power to overclock itself (as long as it is below 80 degrees celsius) for the graphic intensive games.
In short, it really depends on the kind of games you are playing. For best performance for graphic intensive games, you should look to update your psu. Otherwise, if you haven't gotten into those open world/FPS sort of games yet, your psu will suffice for now.