I bet that it’s a typical 4-pin ATX12V and then it’s called Molex Mini-Fit Jr.
https://i5.walmartimages.com/seo/StarTech-com-ATXP4EXT-8-in-8in-ATX12V-4-Pin-P4-CPU-Power-Extension-Cable-Female-to-Male_87b02534-8d1f-42f1-8a6a-d58f746c0614.c78acfd695d940c1207faefeb95e2fbc.jpeg