Let me make some corrections / clarifications.
All fan signals on a common header are % of full speed whether PWM or DCV. Today's MoBos have plenty of Fan Headers, so PSU control is kinda so "last decade"
DCV controls fan speeds by varying the voltage
PWM comtrols fan speeds w/ a constant voltage but by essentially switching the power to fan on / off
The 3rd pin on both is the feedback control, tells the control system how fast the fan is going with either control method. The 4th pin on PWM is the digital control signal
3 pin - https://allpinouts.org/pinouts/connectors/motherboards/motherboard-cpu-3-pin-fan-connector/
4 pin -
http://pinoutguide.com/Motherboard/mb_pwm_fan_pinout.shtml
Both methods have their advantages and disadvantages. PWN historically had better low speed control, tho in recent years DCV has made great strides in this area. PWMs downside has been cost and low speed clicking / hum
Using PWM devices on 3 pin connectors is not recommended.
You want all the fans on any fan hub to be the same speed. Today's MoBo headers can usually do either DCV or PWM with most auto sensing what is attached. NZXT has been emulating many of Phanteks case features, among them the hub. The Phanteks one I am very familiar with... it can take wither a DCV or PWM signal and will power up to 11 3-pin fans giving you a best of both worlds approach ... low cost, no clicking / humming and low speed control. With DCV fans and DCV fan control, you do NOT want to use the provided SATA power cable as the DCV fans will just run at full speed via the 12 power signal. However, you must take note of the amp draw and make sure the total number of fans connected does not exceed the header rating (typically 1 amp) ... with 1200 rpm 140mm fans, you can usually have 6 fans connected.
With PWM signal from MoBo, remember the control is on / off not voltage ... so you CAN to use the SATA power cable for up to 11 fans w/o issue. You wont over draw from the header cause the power cable is supplying power. Now from everything I heard from NZXT Tecg Support, the NZXT fan controller is very much like the Phanteks. I had follow up questions but the didn't respond ... so there are minor differences but not sure of the significance.
But yes, the fan controllers ... at least the oens I have used, are intended to take a PWM signal and control 3-pin fans. Phanteks also does DCV control... dunno about NZXT.
There is never a need to use a 3 pin / 4 -pin converter ... all headers are designed to connect to both so its a waste of money...