Is it the power supply on the computer or is it the computer components which determine energy useage?

I'm wondering if buying a power supply with a greater wattage rating affects the energy used. So, does buying a higher wattage power supply result in an increase of my electricity bill even if the computer components kept the same, thus drawing the same amount of power?
THANKS!!!!! I was going to buy a antec 520W for $55 which was cutting it close with a Phenom II x4 965 + HD Radeon 6870. But I've found a killer deal on newegg for an Antec Earthwatts 750W for $65 with a sale + combo deal.

thanks

power usage is determined by the components of your system; they take what they need. if you buy a new psu, a big consideration is the efficiency of the unit. low-end (quality-wise) psu's are inefficient and waste power by turning it into heat. i suggest a true 80+ percent unit. these are expensive, so don't buy wasted capacity for your system. a good example should give you a 5-year guarantee.
so, in  the end, you may end up using less electricity!!!