Power Supply Cables vs Motherboard with an 8 + 4

rutledgek

I was in my local Microcenter in St. David's last week and bought the parts I would need to build out a machine using a 5950x, 3080 graphics, multiple hard drives etc.

In discussing with the sales tech there, they thought my PSU may be overkill and we dropped from a 1000w to CORSAIR RM850X FM 80+G ATX 2021 which he recommended.

This is the first computer I've built in 20ish years so a lot has changed in that time, including power usage requirements and modular PSUs. I finally started to build it out last night and realized that the motherboard(ASUS ROG STRIX X570E GAM WF II) has an 8 + 4 pin power connectors while the power supply only has two 8 chords. Since I am not sure what this all entails, my research suggests that +4 is used for power-hungry CPUs and/or extreme overclocking. I wanted to ask here in case I need to return and swap out my PSU before I get it all together and installed.

Any help would be appreciated.

PowerSpec_MikeW

@rutledgek

You don't need to connect it, it's supplemental power. Socket power is capped at 142W's, a single 8 Pin can provide up to 336W. The only reason you would want the supplemental power connected, is it distributes the load somewhat. Cleaner power delivery, lower temperatures on the 12V's supplying power, since there would be 6 instead of 4. Really, you need a high end board and high grade PWM to really take advantage of this. It's meant for extreme overclocking.

rutledgek

Thanks. I still kind of regret not getting the larger psu. long range plan is to run a few vms on it so I was thinking of adding a second GPU. 850 wouldn't be enough there.

PowerSpec_MikeW

@rutledgek

Yes, I would upgrade to the 1000W if you doubled up on the 3080's.

rutledgek

I think I might. And thank you for your help. One final question, at least i hope. I have the corsair AIO 150 pro xt The instructions say to connect the tach cable to the CPU fan header. I was able to get it one correctly, but the AIO tach cable is a 3-pin connector and the MB CPU fan header is 4. From the diagram on the MB manual, it looks like the PWM pin is the one that is not connected. The other three are ground, fan power, and fan in.

PowerSpec_MikeW

@rutledgek

Ground - 12V - RPM Sensor - PWM. 3 pin on a pin header is fine. The fan will be DC controlled instead of PWM controlled. With the Corsair AIO it's mainly using the 3 pin to report the pump RPM and avoid a CPU_FAN error. The pump will generally govern itself, it has SATA power directly from the PSU.

The other header you'll see is AIO_PUMP or W_PUMP. You'll use these with some AIO coolers, where the radiator fans are required to be connected to a fan header. So you'll put your pump on the AIO_PUMP and radiator fans on the CPU_FAN. Generally those two headers have no thermal control as you want your water pumps to run at 100%.