if you don't want to look for a power supply specific to your computer, get a 500-600w one, you'll most likely never need more than that
don't buy a really cheap 500w power supply with a shit brandname like "fastpower" or some shit
if the price seems too good to be true it is. powersupplies made by shit chinese brands although they do give the power will break really easily, and if a powersupply burns out in your computer it's most likely gonna damage a lot of stuff inside too
if you're willing to go for a quality one, you can check out some guides on the internet as to which ones are really sustainable and stuff. i'm pretty sure corsair make some of the best
don't worry about it having the right amount of cables too much since you can just buy adapters for like 5 dollars
and yes it turns out graphics cards do actually need electricity to work