Psychogenic Endurance is a Tier Four psionic discipline that increases the END stat by 2 for a duration of 2 minutes + 1 minute per PSI, up to a maximum of 8.
Extra hit points are always helpful, especially when going against particularly tough opponents. The extra hit points are lost when the power runs out, but this will never reduce you to below 1 hit point.
On higher difficulty levels, each point of Endurance gives you fewer hit points (than what you get at lower difficulty levels), making this power arguably less valuable at higher difficulty levels. On the other hand, since you have many fewer hit points to begin with, the additional ones, even if fewer in number, may be proportionally more valuable to you.