Fat Hdmi Xbox 360 Fans, What is the fan header in the fat hdmi xbox 360? Options

[pogonoforysci2]

Hi, I'm planning to move my fat hdmi xbox 360 to a custom case and change the cpu and gpu heatsinks to big pc cpu ones at the same time. I bought a damaged motherboard for measuring and fitting and I can see that it has a 3 pin fan connector (it's also a hdmi board). I always thought that the fans are PWM (so 4 pin) as they change their speed depending on the console work load. The fans that I got with the heatsinks that I want to use are all 4 pin PWM. Will they work with the 3 pin header and will they adjust their speed like the original fans or just go at full blast all the time. Also is it OK if I run 3 fans (1x 92mm, 2x 120mm) from the motherboards fan header? I've read somewhere that xbox 360 power brick provides a limited amount of power and connecting too many after market bits may put a strain on it (I've seen set ups where people used external pc power supplies to power the fans because of that). Is that true? If so will I be OK with the 3 fans that I want to install??