I know third party cards provide overclocking tools, but I don't know if you can undervolt. Also I was talking specifically about NVIDIA for something that works with all cards.The begs the question as to whether Nvidia cards *need* tools for power management, or whether 'they just work™'.
Anyway, the 3rd party cards usually have tools like https://www.hardocp.com/article/2015/09/01/asus_gtx_980_ti_strix_dciii_oc_video_card_review/4