On your case, which does come with a open area under the psu, you should fit it with the fan facing downwards, power cable going out the back ofc.
The only reason for you to put it with the fan facing upwards, would be if you need any extra exhaust of hot air (will make the psu hotter, but would also remove the hot air out the back of the psu. Though it's rarely recommended to do it with the fan facing upwards.