I’m unaware of an actual specification for the orientation of the connector, and I’ve seen things listed both ways online, so please pay attention to the description here to make sure you order the right part.
I’m assuming you want the adapter’s receptacle to face down, if so please order based on the orientation of the center pin as you have your PSU mounted. If your PSU, when mounted, has the center pin above the other pins, then order the UP option. If your PSU, when mounted, has the center pin below the other pins, then please order the DOWN option.