The computer draws what it needs from the PSU. Typical modern computer runs about 150-180w at idle. Gaming video cards under load can bump that up quite a bit. No real benefit from going overboard on size of PSU. Should stick to brands with good reputation, avoiding cheapest ones.
Ok thanks didn't know that. I guess if I upgrade to a Nvidia that plugs into PSU I best check it's needs. It's nothing high power no fan just heat sinks.