What type of fans can I control with a fan controller ?

Hello people,

I am rather confused about what type of fans you can actually control with a PC fan controller ?
I have just bought a Scythe Slip Stream 120mm, 110 CFM fan which i put on the side of my case (HAF 912 i think)
and it is extremely loud... for me anyway. When I am not gaming I don't need it to cool my PC therefore I could lower the RPM so
it is less noisy.

I'm talking about this fan
http://www.newegg.com/Product/Prod [...] 6835185060

It has a 3 pin connection which could connect to the motherboard (I only have 1 Chassis Fan connection on my mobo though and it's already in use) but i always try to hook my fans onto the PSU. It came with the 3 pin to 4 pin MOLEX converter so i was good to go.

I have the following 'dilemma' :

I was telling my friend that i will probably get a fan controller so i can turn the fan down a bit so it isn't that noisy and he said it is already running on it's minimum/lowest RPM. Is he right ? (He is quite a techie guy so i should believe him but this time I don't really know. I always thought if the fan is not connected to the motherboard but instead connected straight to the PSU it gets max voltage and power therefore the max RPM. )
Then he told me I could not turn the fan down with a fan controller . That's what confuses me

1.So can someone please explain to me what type of fans can be controlled via a fan controller?
2. Can the above mentioned fan be controlled via a fan controller?

Can someone help ?

Thank You in advance !