Although it is AM4 socket, Dell is lazy enough not to design a proper AM4 oem cooler for it. So the motherboard actually uses intel socket heatsink mounting hole spacing (square 75x75 mm).  Dell does the same thing in Aurora Ryzen edition: amd cpu socket, but hybrid intel heatsink spacing (LGA1151).  Why?  It is simply not worth Dell effort to invest in a proper oem am4 heatsink because Dell makes so fewer amd pc compared to vast number of intel pc. [IMAGE] 5055 uses same pancake heatsink assembly as 5050 which is intel based.   [IMAGE] having said that, you can just try to replace your oem cpu fan w a more quiet 80x80 mm non-Dell fan while keeping the heatsink (NB: many non-Dell fan may throw a bios startup error), or you can replace the whole cooler w a low profile one (you have 5055 SFF) but bear in mind Dell heatsink uses M3 thread backplate built in chassis floor.  New heatsink needs to be c/w M3 backplate too. PS AM4 heatsink spacing is rectangular.  The AM4 socket specifies the 4 holes for fastening the heatsink to the motherboard to be placed in the corners of a rectangle with a lateral length of 54×90 mm. The 4 holes for fastening the heatsink to the motherboard are placed in a square with a lateral length of 75 mm for Intel's sockets LGA 1156, LGA 1155, LGA 1150, LGA 1151 and LGA 1200  
Dell Optiplex 5055 With high-quality CPU cooler. I would like to replace the existing cooler with a higher quality cooler that should be very quiet.Since it is an AMD AM4 socket I am not sure what alternatives there are that also fit. With kind regardsChris
Dell Optiplex 5055 with new CPU Fan.