It seems your Dell has a 305 watt PSU. The GT 730 requires 300w PSU - minimum. The PSUs including in these machines are cheap and often cannot output the wattage they claim to output. Some can even explode under load, frying everything in your PC. I'd say it outputs 250w - max.
I'd get a new PSU before the GPU. While your PSU just meets the required wattage, your PC can shut down or freeze becuase of low power. Fortunately, the PSU in your PC is not propietary. You can fit any standard ATX PSU in it. I'd recommend the EVGA W1 500W or 430w -
http://www.newegg.com/Product/Product.aspx?Item=N82E16817438015&cm_re=evga_430-_-17-438-015-_-Product
There is also a 500w option too. Just don't cheap out and get something crappy like a non-branded PSU. Don't get the Corsair CX series though.
Hope I helped.