Those two cards would be well suited to your system and should work just fine, however your PSU is only just enough. Most likely your PSU would do the job and not give any issues, however, there is always that small chance of it failing and potentially damaging other components in the process.
So you can either;
Take a chance with your current PSU.
Replace your PSU with a slightly bigger unit of reasonable quality.
Or get a GT 1030, which is slightly below the GTX 750 in performance but only requires 30w so would be fine with your current PSU.