240 / 220 is almost always slightly more efficient, since you're drawing less current (which means less resistive losses in the wiring). Although this effect is minuscule. It's also far easier and cheaper to get PSUs that deliver the load with 240.

It is technically possible that your PSU can change your mining rate - if you're overclocking and have one of the really old S7s. Apart from that, unless the PSU gets wobbly (way less than 12v output), there's no difference to hash rates.