It'll work fine with you PSU.  Check out this YouTube video for fit (I wasn't sure if the heatsink is still too tall).
I have a Dell optiplex 990 SFF, and I am thinking about purchasing an RX 6400 low profile and putting it in the optiplex. Would this work? Card wattage is rated at 53W
RX 6400 in an Optiplex 990