Power stations. Is there a rule of thumb on if you want a 450w or 850w?
Tom's Hardware has a formula but it looks extremely detailed. Is too much power bad?
Too much power can lead to a little more heat than desired but it is not a bad thing unless you are hypersensitive about your utility bill. The video cards are getting more power hungry. I bought an ATI 5770 video card that consumes only 120 watts so I have a 550 watt power supply with a 9550 quad processor.
450 watts might run your video card just fine but that i7 might need more than your last processor. Check the i7 specs for the wattage needed. I think it is around 130 watts.
So, add in the processor of 130 watts and what your video card needs and another 100 watts or so for disk drives, memory, and the motherboard and you’ll have a ball park number. You can google for your videocard’s wattage requirements.
Don’t forget that every video card requires certain connectors from the power supply, such as a single 6 pin or single 8 pin or two 6 pins.
They are switching supplies, so your computer will never have “too much” power.
You can, however, waste lots of money buying a larger supply than you need.
The main factor is going to be your video card.
Typically a 500W supply would be adequate, unless you’re building a gaming rig with a very high end video card.
Definitely buy a quality brand. This is one component that you don’t want to get the cheapest one you can find.