Hey,
I suggest you to get gt1030 2gb instead of gt 730.It will be worth the upgrade.
NVIDIA GeForce GT 1030 2gb is a great card for 99$ and consumes 37 watts only at its peak.Also it will be well worth for the price you are going to pay for GT730.System requires you to have 300 watts power supply only.
I personally in your place could have saved money and put my money into some current gen card like NVIDIA GeForce GT 1030. Why are you going for previous 3rd generation card?
You wont be able to enjoy modern games well with GT730.As you can enjoy with NVIDIA GeForce GT 1030 like CS-GO , DOTA 2 in e-Sports or titles you want to play in medium settings at 1080p at least.
With NVIDIA GeForce GT 1030 , you wont need to upgrade your power supply too.FPS 500 watts will be enough.
Thank you,
Ishaan