Expreview has used Xigmatek's Midgard case to test which fan configuration gives the best thermal results in cases with a bottom-mounted power supply. The site tested four different fan configurations to compare temperatures and concludes that the most logic way to mount the fans gives the best results. The lowest temperatures were achieved by using a front fan to pull in cool air while top and rear fans exhaust hot air, while the worst results were achieved by letting all three fans pull in cool air. You can check out the results over here.
From the test,we get to know that for most of power supply underneath case,if the rear fan adopts air outtake setting,it can get a relative ideal cooling performance,especially it will have comparatively much effect on CPU cooling and case temperature,there will be gap of up to 5℃ with CPU
temperature,while it doesn’t make much difference whether the top fan features air intake or outtake settings.
In addition,no matter in what kind of fan collocations,there will be minor help towards graphics cooling,the temperature change of 1℃ can be neglectful.