Which diode to choose to prevent molex PC PSU powered HUB to be damaged or backfeed
Any shcottky diode will do fine.

You only have to consider the current rating. To be on the safe edge, it should be 5A or more.

But if you know that the devices connected to the Hub wouldn't draw 500 mA each (most devices don't), you can use a diode with a smaller current rating.