If your graphics card is not getting enough power you’ll experience frustrating things like your game crashing and general system instability. Nvidia advises at least a 650W for your PSU. To be on the safe side, it’s good to add 100-150 buffer to your PSU, allowing for future flexibility should you wish to add more fans, drives or add-ins in the future. This is also advisable if your monitor is particularly demanding and you’re playing graphic heavy games.