Fan upgrade for Delta DPS-770 (Server module)

[Phas3L0ck]

I have a pair of DPS-770 power modules in my server (GB_C variant) and I've been looking to replace the 40mm fan in both of them to reduce noise. But for some odd reason, the module won't start with any fan other than the original... both the OEM fan and the new one I bought are 4-wire, and most likely PWM as far as I know.

These are the fans involved:

NIDEC W40S12BS1D5-57 - OEM fan; 61db noise, 22,500RPM, 28.6CFM, 1.05A  (and loud as H3LL with the high-pitched motor frequency and bearing noise)

AVC DB04028B12U (P029 variant; PWM) - intended replacement fan; 54db noise, 13,000RPM, 23.8CFM, 0.66A  (dual ball-bearing; softer motor noise and reasonably quieter)

 

They both have the same connector, and with the AVC fan I tried all different combinations swapping pins around, but nothing seems to provide the DPS-770 with the sensor input it was designed to get from the NIDEC fan.

The AVC fan spins as it should when the module is powered on, but the unit won't activate to provide power to my server as a result of the fan sensor in the module seeing a fault and shuts down the module entirely.

  Update: I guess I had a bad variant of AVC's fan (P029) since one turned out to work fine with the right wire arrangement, while the other may have a bad speed sensor. There are so many variants available but no information on which one does what.

 

I ordered different fans to see if anything else would work, and a pair of San Ace 9GA0412P3J01 fans work mostly right, but for some odd reason, the PWM/control signal isn't compatible with these power modules.

WHAT is going on here???

 

Photos of the power module and fan are here: