Yes your certainly do need a separate PSU for the spindle and steppers / breakout board. The breakout board looks like it has a relay on there so the idea is to run the power for the spindle through the breakout board, but it is just acting as a switch so the PC can turn the spindle on and off. I don't bother myself.

If you are not familiar with electronics then be very careful when playing with PSUs as mains voltage can kill.