Given 2 capacitors; a 330uF with 89mohm ESR, and a 4.2uF with a 7mohm ESR, I'd like to calculate the total capacitance/ESR when in parallel with a 200kHz frequency.

Convert C into X using (1/2*PI*f*C)

X = 0.003215251

Therefore, Impedance Z1 is the ESR for the Real part of Z plus X for the imaginary part.

Z1 = 0.089 - 0.003215j

I perform the same on the other capacitor and get

Z2 = 0.007 - 0.25262j

Then I use the impedance formula for parallel impedance; 1/((1/Z1)+(1/Z2)), and get

Z = 0.07686-0.0295833i

So ESR is the Real(Z) part = 76.86mohm?

And X is the Imaginary(Z) = 0.0295833mohm.

So C is (1/2*PI*f*X) = 35.865uF

That doesn't seem right. There is a 330uF and a 4.7uF in parallel. It doesn't seem right that the total capacitance has dropped to 35.865uF when in parallel.