P=V x I (potencia es igual a voltaje por corriente). Pero si tienes ventiladores de mas lo suyo es que los conectes directamente a la fuente, no a la placa.
Acabo de mirar en tu palca y dice esto:
"• Please refer to your processor's official website or consult your vendor to find
recommended CPU heatsink.
• These connectors support Smart Fan Control with liner mode. The Command
Center utility can be installed to automatically control the fan speeds according to
the CPU's and system's temperature.
•
If there are not enough ports on the motherboard to connect all system fans,
adapters are available to connect a fan directly to a power supply.• Before first boot up, ensure that there are no cables impeding any fan blades."
Lo que he puesto en negrita es lo que te comentaba, ventiladores de mas, a la PSU.
Edito: lo que sacado de aqui:
http://www.manualslib.com/manual/831785/Msi-Z97m-G43.html?page=35 
