just wondering how anyone using pc fans for ventilation safely powers them?

multi voltage adapters

I use the very thing they were designed to be run off.... A pc power supply.
It is air-cooled, has enormous capacity, has it's own internal fuses, and will run more fans than you have wire to connect them all up.
Just take the bunch of wires leaving the power supply, cross the green wire with any of the black ones, and hey-presto the unit powers up without the computer. Easy-peasy.

I am useing the next size up ,,the ones they fit into steel workstations,,,stright of 240v,worth looking out for