Easier to just remove the PWM line on the stock fan (I prefer to pull the connector out of the plug then electrical tape it, some folks might prefer to just cut it as that's easier), then it runs at 100% all the time for best cooling.
Not all the time some fans will stop spinning if you remove that PWM wire. and others will spin 100% RPM it depends on the fans controller chip built into the fan. so like I said it depends on what fan.
Any fan that does not run 100% with the PWM line open is BROKEN (either by design or by failure), and does not meet the SPECIFICATION for PWM fans (the spec specifically calls for the fan to have an internal pull-up on that line and the DRIVER to the line to be open-collector).
But yes, I did test it to be sure, having seen way too many items fail to meet specs over the years....