In the depths of the Internet, I found a pinout for the twin Delta DPS-600RB power supply. It just so happens that I bought this and the same as the author of the topic :)
I am adding the written signals of the tape connecting the power supply with the contact panel. Maybe it will be useful to someone. The panel is the only place that connects the ground to the housing. When connecting the power supplies in series, it may be necessary to disconnect the housing from the ground.
On a trial basis, I found the RS RTN signal which, when connected to ground, slows down the fan. When the power supply is heated with a dryer, the fan speeds up, so the speed control system seems to work. But I have not found a description of the RS RTN signal anywhere - maybe someone knows what it is?
I warmly welcome. I wanted to share a datasheet unearthed in the depths of the Internet. Applies to the turbines in the DPS-600QB power supply. I think it might come in handy for solving the volume problem. It is probably not an official document, but it seems quite accurate.