That psu has 19A on the 12v rail and 21A on the 3.3v. That's a really old design, from the AT days, well before ATX standards. Modern pcs use primarily 12v for everything, with the minor rails for things like the hdd etc. My 520w has 40A on the 12v rail by comparison, and it's considered last generation and not Haswell compatible.
Sorry, but that psu is a dinosaur and will end up crippling any gpu bigger than what you have, and maybe even other components too. The GTX730 recommends a 300w psu with 20A on the 12v rail. This is how underpowered that psu is. In this case, it's the Amperage that's important. The recommendation takes into consideration the top end of usage, so if you don't oc, don't push the pc to extremes, you'd barely be ok, but for how long is a different story. You'll be maxing out the 12v rail constantly, and it's not a good quality psu to begin with.
Should you replace it now? Yes, as soon as possible, making sure any pc use is minimal until then. As far as size goes, plan the new psu around any possible future gpu upgrade. For that build, a seasonic 520w, antec hcg 520w, xfx 550w, would be perfect, and relatively inexpensive if you watch for sales.