what exact product number of the Noctua fan?
in 40x40x20cm size of fans Noctua has two kind of electric specifications 5V and 12V. Three wires (one for a rpm regulator)
but
original fans in
RS819 has been manufactured by Sunon with part no MB40201V2-0000-A99 = 12V/50mA, two wires red(+), black(-)
for such hobby, as is tuning of computers is highly recommended usage of multimeter and be pretty sure, what are you doing. Just to be sure. So don’t waste your time and read before this replacement FAN product specifications. Because you will find, that the Sunon has >30% more airflow capacity than the same Noctua, finally no variable rpm. OFC Noctua is more silent (but in this case with low airflow).