no problem.
two points:
- just an advice, dont run it long without any equipment connected.
psu's are designed to run with a minimum amount of current consumption (load), else they have a tendency to shutdown. Never burned one thou, so you shouldnt have any issues there, imo.
- three wire fans have two for power, and one for RPM monitoring, usually red and black for power, green or yellow for RPM.
If they are the beasts you say they are, you should try to get the amps and volts rating , on the back of them.
If they are 12v, you can connect them directly into the 12v rail on the psu, yellow and black (ground). If 24v, you can do the same, but they will run undervolted, which is probably a good thing as 300 cfm fans are noisy as hell.
Or, you can get a 24v regulator at an eletronics store. Or , if they are 12v, and under 20W (V*I) , a sunbeam rheobus can do the trick.
300 and 550 cfm are overkill , imho.
