^^ A molex connector, is the same power connector that is used for your Disk drives/Optical drives. Your power supply should have enough of these molex connectors. If your gfx card needs a molex connector, simply utilise one of the unused ones.
A 300W PSU is a bit low, especially since it is a generic brand and not a quality one like Antec, FSP, etc. If possible, try getting a Powersafe 400W PSU. Should cost somewhere around ~ 1.4K. You can try running the card with your current PSU. However if you start facing random problems/blue screens, rebooting, hanging, etc , you'll know your PSU is being stretched past its limit.