all raisers to main PSU. Only GPUs to secondary PSU
Yes. Essentially the same PSU that powers the motherboard also powers the risers and accessories. The auxillary PSU is just for the VGA power inputs on the cards. Just be sure if you are using SATA or 4-pin molex connectors, to not use more than two connectors per PSU cable max to power risers. Any more than that is a fire hazard since it will overdraw the capacity of the the cable and it could damage the connectors, the cable or the PSU.
Thank you very much @hanskan and @Vann. I really appreciate Vann's detailed info which really help me alot. Yes, I understand that SATA molex connector had limited wattage output, so at max 2 connections to usb risers, I will take note about it.
All the best to your mining