The power supply lets a small trickle of power to flow to the mobo at all times to let it sit in standby when it's not on. When you press the power button, the mobo sends a signal to send power to all systems and power up its own fan. Case fans can either be powered by your motherboard (you can control the RPM with this method) or you can use a molex (the kind of power plug IDE devices use) to 3 pin case fan adapter cable. There is a trick you can do by shorting two wires on the mobo connector to fool the power supply into thinking the mobo is telling it to power on, but I don't see why you would need to test your PSU/case fans. If they don't work when you power it on for the first time, the computer won't melt if it doesn't have those fans blowing for the 10 seconds it takes to check them.