Good power supplies start at about 70. I need to replace my 400watt power supply for something bigger like 480watt. My power supply is not enough for my system. When shopping for a power supply, u need to look at stability of voltage when under load. A cheap power supply doesn't have that and could do more harm then good. If your power supply fluctuates in voltage to much it can either lockup, blow out MB, CPU or even the video card. Most of the time your computer will just lockup randomly.
The power supply's I recommend are the true power made by Antec. Again a $30 400watt power supply is nothing like a $70 400 watt power supply. U get what u pay for, remember that.