I *may* be buying a new pre built system soon, but I'm not sure if the power supply which comes with it will be able to deliver enough power. The system is an HP Z400 which comes with an Intel W3520, 6GB of ECC ram, and 2 fans (1 of which is CPU). What I plan to install is 2 HDD (1TB WD and 500GB Hitachi), 120GB Kingstone SSD, 1 120mm fan and an EVGA gtx 650 (with maybe a 250mhz overclock). The power supply which comes with the system is a 475watt 85% efficient power supply, but I don't think it'll be enough to power all that. Can someone with more knowledge about power tell me if the 475w power supply can support all the hardware, and if it can, approx. how much power will be left over?
Thank you to whomever answers this, and if I didn't make sense, tell me so I can attempt to re-write this in a way which may make more sense.
I already own the gtx 650. If I got the 750 I'd be paying $130+ for a new graphics card which would only get me around 10-30fps more,which isn't worth it to me.
A 475w PSU should have no trouble supporting that, if its like a regular PSU.
Apparently this is the build in psu http://www.ctsestore.com/hp-475w-power-supply-delta-dps-475cb-1-468930-001-480720-001-xw4600-tower it has 450w max on the 12V rail, so even a decent GPU shouldnt be a problem. It only has one 6pin though. Its build by Delta Electronics, so it should be decent.
Peak power usage without the GPU should be around 200w
You could use pcpartpicker.com to estimate your wattage (I believe they estimate the max load). It's easy, all you need is choose parts you owned from their list. There are also other specialized websites for calculating "powa" too. :)
How you use PSU efficiently depends on what you use your PC for the most. Is it gaming, working with spreadsheets, editing videos, etc? Which is the longer period you'll be using your PC for? The more you need your parts (CPU, GPU, etc) to work, the more power they draw. Eg a GPU power consumption is 60W at idle and 100W at maximum load.
So to answer, is this PSU have enough power? You need to know the power consumption at maximum load of all your components. When all at max load you know you can't have any other power load from your parts. Not enough juice will results in shut down or even damage your components. But you don't need to worry with quality PSU nowadays cause they have overload protection.
To know the efficiency of your PSU, you'll need to know the efficiency graph of it. This is related to how you uses the PC as I mentioned above, you want to be working/ gaming near the peak efficiency. Each PSU have different efficiency rate and curve, most are not efficient at low loads and usually at max efficiency at around half their max load. Just target around the peak when you're in the commonly used condition.