I spent ages tracking down a properly silent PSU for a project that now isn't happening :-(
Silverstone EFN-300 ATX PSU (also known as ST30NF); 300w. Very heavy, massive heatsinks, has no fans and designed to run 100% silent. Think this is the model for more info: https://www.silverstonetek.com/legacy.php?area=en&model=st30nf&tno=2
PM me any interest?