I use 200mg of Source Naturals brand Huperzine A daily.
While it is a good point to look at adrenal function, unfortunately, this is not the answer for all of us. For many of us it's autoimmune, triggered by infections like EBV or toxic exposures.
My adrenals weren't functioning well to begin with, before my orthostatic intolerance. I read everything I could on "adrenal fatigue" and was using every strategy suggested and nothing helped until I went on replacement dose hydrocortisone in 2016.
Prior to 2016 to this day, I've taken high doses of vitamin C, including IV vitamin C as well as every other nutrient you mention. I took Vital Nutrients Adrenal Support too.
None of this fixed my hyper POTS. I was tested and my doctors prescribed a beta blocker and pyridostigmine, then the neostigmine and Huperzine A. My specialists tested me and found I had positive adrenergic and muscarinic antibodies. Treatment with Rituximab greatly improved my POTS
In the meantime as we worked to beat back 5 viruses and 2 atypical pneumonias, and my immune system was supported by LDN and IVIG and I worked on mitochondrial repair, my adrenals slowly l began working better and I gradually tapered off the hydrocortisone.
So, while your message may be valid for a few, I am not convinced that autoimmunity and infections aren't driving POTS for the rest of us.