Most 4090's come with a 4 8-pin to 16-pin adapter. But PSU-ports are finite (Trying to install 2 4090's into one machine). is it safe to use a 3 8-pin instead of one that's 4? Or does it matter?
This 30 dollar cable is supported by the vendor lol.
Not everyone will have a 4090, for example I have a 4070TI.
All the guys at MC are using the corsair cable and RMX power supplies no issues.
4090's are 450w cards nominally. That's just fine with 3x 8pins as a 8pin is rated for 150w, but in reality can handle closer to 180w. The card knows how much power is supplied. If the card senses the 4th 8pin, it loosens up the power limits and allows anywhere upto 600w, depending on the manufacturer, but generally is closer to 520w.
If using the cards for production work, better to keep them at the 450w limits anyway, the gains due to the higher boosts aren't offset by the heat/power requirements of the higher boosts.
This would be a great time for the original poster to actually say what their PSU is, because we're all arguing theoreticals since the initial question was woefully lacking in actual information provided about this situation.