How to work out my hardware's hashrate power Using my existing hardware, I want to work out which altcoin is still profitable to mine.

I have found this link:

http://dustcoin.com/mining

But don't know which values to enter into the boxes at the bottom of that page.


How do I work out the SHA-256 and scrypt hashrate
For the Power(W) box, do I enter in my computers PSU wattage? I think it's 650w
For the Power Cost ($/kWh) box, do I check my electricity bill to find out how much I am paying per kWh?
How do I work out the SHA-256 and scrypt hashrate


You can look up your hardware e.g. here (BTC) and here (LTC). But I think it's much easier and more accurate to just try mining different coins for couple hours and measure hashrate directly.


  For the Power(W) box, do I enter in my computers PSU wattage? I think it's 650w


PSU wattage is max. power it can supply, so it poses upper bound on PCs consumption. 
To get accurate measurements, you can use something like Kill-a-Watt. Or you can look up TDP of individual components: CPU's, GPU's and ASIS's power consumption is usually listed in their specs, and motherboard+RAM+HDD together usually use around 50W.


  For the Power Cost ($/kWh) box, do I check my electricity bill to find out how much I am paying per kWh?


Yes.