i have never used one with AC, personally i would not be keen on using a cheap AC volt adjuster either
which is why i suggested a 12VDC fan, it would likely have a much lower setting right out of the box and be designed to run slower
(similar to how the tower the OP has decided on is also DC)
and using 12VDC, it would only need slight undervoltage for a noticeable decrease in speed
which would likely be low anyway on low setting
maybe i will but that fan just to find out what they are like and use as portable
i do have milwaukee 18V portable fan but that is a bit noisy, but it is not built to be quiet but does its job well