does anyone know what kinda adapter cable i need for my molex fan cable so that it can be plugged to mobo and speed adjusted?
i read somewhere that the fan would not report its running speed but i hope the speed (because its originally molex cable only) can still be adjusted, anyone knows?
An adapter cable wouldn't enable your fan to be speed adjusted, you don't need one. The fan has a motor inside, and how you can adjust fan speed depends on what is available to drive the motor. Btw, case fans don't have "molex cables," in fact molex refers to a specific connector type, which connects the PSU to larger equipment. This is what is known as a molex: http://en.wikipedia.org/wiki/File:Molex_female_connecto...
If the fan has three or four cables, as most fans sold nowadays are, then it is designed to report its speed. You can get some basic info on fans and controlling fan speed from good old Wikipedia: http://en.wikipedia.org/wiki/Fan_control
You can always control fan speed, because this only requires adjusting the input voltage. Whether the speed of the fan can be controlled by software depends on the motherboard, not the fan or its connection. But if you find out that your motherboard isn't designed to control fan speeds (it usually will control at least the CPU fan speed), you can buy a fan speed controller to do the job.
"Molex cable" doesn't exist, molex is a type of connector. Most fans use small three-pin or four-pin connectors, like the one in the middle below. It could also be called a molex connector (KK family), but molex usually refers to the Molex 8981 you see on either end. Those you don't see on fans, although you can connect a fan molex connector (KK) to the molex 8981, which is the one connected to the wires coming out of your PSU.
That's just weird, to me. The only reasons I can think of to put that big of a connector on such a small fan are (1) it draws a lot of current, which it shouldn't (2) to be able to connect it directly to the PSU (99% this is why).
Yes to your question, here's the product description:
Power a cooling fan directly from your motherboard to allow for variable speed regulation with this 3-pin motherboard to 4-pin Molex adapter. It includes both male and female Molex connectors to attach to a variety of fans.
The answer to your question certainly is yes, you can use an adapter to connect a mobo 3- or 4-pin SYS_FANx pinout port to a case fan that came with a 4-pin Molex connector. The Amazon item that debianos linked to does the job. Just do NOT connect the second Molex 4-pin connector to anything else!
Your case fan has a black lead for Ground and a red one for the +VDC supply. The voltage on the red line is varied from 0 to 12 VDC to achieve speed control. When simply plugged into a Molex output from the PSU it gets +12 VDC always and runs full speed. Using the adapter will connect that fan red wire to the mobo pin normally feeding the red lead of a 3-pin fan, which has the same function except that the mobo can vary the voltage on the red line. At the mobo connector the third pin is for a yellow lead feeding a fan speed signal (as pulses) back to the mobo. Your fan does not provide this, so there is no connection to the third mobo pin, and no way for the mobo to display the fan's speed. In fact, in BIOS where you configure that SYS_FAN port, you may need to tell it to Ignore that fan's speed just so it does not panic when it detects ZERO speed (no signal).
IF you happen to connect via the adapter to a mobo SYS_FAN pinout with 4 pins, you will need to make one other BIOS setting. On 4-pin connectors the fan configuration seeds to be set to 4-pin or PWM mode IF you are really using a modern 4-pin fan, OR to 3-pin mode if you are not. Setting to 3-pin mode ensures that the mono controller will do its work to vary the voltage on the (red) +VDC line to achieve speed control.