it never hurts to run the power supplies in as cool an environment as possible. That having been said, moving the power supply complicates the installation and future maintenance of the printer by separating the printer from a major component. To determine the environment that the integral power supply lives in, I instrumented the enclosure in the vicinity of the power supply and observed the following:
Enclosure temperature never got hotter that 35°C with a bed temp on 70°C. 70°C is what I use for PLA and PTEG. On ABS I run bed temperature of 100°C. The internal Enclosure temp is <45°C for ABS. This is using the restrictor orifice. If you overboard all the filtered air, the temperature should lower another 5°C. The HEPA filter fan used was San Ace P/N 9G0612G101 moving 65 CFM air out of the enclosure. I concluded the trade-off between running a cooler power supply vs ease of maintenance favored easy of maintenance since 45°C is within the typical operating range (<50°C) an ATX power supply.