With the setup in your specs, I would say 300W isnt enough or close, as you are right now. Depending on the quality of the PSU.
If its one that came with a pre-built machine for example, then I would say dont chance OCing.
You may want to invest in a better PSU.
to give you an idea what kind of wattage you need: eXtreme Power Supply Calculator
But remember, 12V rail Amperage is the most important thing. NOT Watts.
For your setup ,it will consume around 200W avg. But once you start overclocking, the power draw will increase significantly.
But youll probably want around 32Amps at least to be nice and safe.
Perhaps upgrading to something like a 400 or 450W Corsair would be a great help, and give you some overhead.