CPUの補助電源8+4PINはLN2のようなOCしない限り8PINだけつければいい
from 自作PC build（2022）
基本いらないらしい
@Yacamochi_db: 最近のCPU用コネクタって「8 + 4」だったり「8 + 8」だったりするけど、i9 9900Kを5 GHzにオーバークロックして動画エンコードするくらいなら「8」だけで全然余裕だから、4本足りないからって気にする必要は（ほぼ）ない。
https://pbs.twimg.com/media/D0Yzym-V4AACQrb.pnghttps://pbs.twimg.com/media/D0YzzjDUwAE65KU.png
@Yacamochi_db: @from_AviciHell 実際に試してないので何ともですが、5.3 GHz以上に行くなら必要かも。オーバークロック競技向けですね～w
https://superuser.com/questions/1379482/do-i-need-both-the-8-pin-and-4-pin-cpu-power-plug-for-my-msi-b450-pro-carbon
2018年の回答
From experience, it suffices to install the 8 pin connector on the left.
The right 4-pin-connector is basically a redundancy that the CPU may draw upon under extreme load most likely only relevant when you do extreme overclocking.
(The board manufacturers most likely also build in some more extra room in case the next CPU generation needs more power.)
So only connect the 2 ports (CPU_PWR_1) on the left, and leave the right one (CPU_PWR_2) empty. If your system won't boot or doesn't run stable, only then you should consider buying the extra cable or upgrading your PSU.
https://www.bestbuy.com/site/questions/msi-mpg-z490-gaming-edge-wifi-socket-lga1200-usb-c-gen1-intel-motherboard-with-led-lighting/6412362/question/c7920985-ae1f-3333-b322-0bf3a3ce7f74
The 4 pin is only necessary if you are doing extreme overclocking, such as LN2. Otherwise the 8 pin will provide all the power you will need.