All games are different. So while one game may hit the cpu so hard to can not feed the video card data fast enough, another game may hit the video card so hard the cpu would be waiting.
I do not think it will be too bad with a 650 as it is a mid end card.
An image of the power supply sticker can go a long way.
The important part is in red. If you have one rail, we need its rating, with 2+, you need the combined(not a simple add operation). Why a 300 watt power supply? because I had one handy to take an image of
This little thing even has the 6 pin PCI-E plug.