After Dean's year ended, and he was dragged to Hell, Sam became obsessed on avenging his brother, so much so, that he almost turned himself into a pitch black eyed demon. Due to his vulnerability after Dean's death, Ruby had the opportunity to manipulate Sam, by claiming it was the only way he could avenge his brother. Even after Dean returned from Hell, Sam was unwilling to let the desire for vengeance go, and he continued using his demon powers secretly. After the imprisonment of Lucifer in the end of season 5, that was the last we heard of Sam's demonic powers up until now.
How does Sam feel towards Jack?
Jared Padalecki explained in this year's Comic Con, what we should expect from Sam Winchester in relation to the new born Nephilim, Jack, in season 13.
This time, he will be trying to cope with the loss of his mother and Castiel, by attempting to solve compassionately the "Jack dilemma". He will also not give up the belief that Mary Winchester might still be alive. He will attempt to nurture Jack, and guide him to use his powers for the better. He will also try to convince him to reopen the rift in order to give Mary a chance to get out, in case she is alive. Sam's empathy, towards Jack, comes from a state of understanding how he feels, and this will cause a lot of friction between the brothers (since Dean sees him as a being that needs to be vanquished).
Furthermore, according to Jared Padalecki, he will relate this situation to his own past, where he possessed demonic powers. This can be an opportunity for these powers to make a comeback in this story arch.
However, in this season Jared revealed that Sam Winchester, instead of being afraid of accepting his powers, will be "awakened" about them being a part of who he truly is (what's important is how he uses them).
What does it mean to have demon powers?
Initially, Sam's powers were manifested solely as a form of heightened senses, allowing him to sense the presence of Supernatural beings. Sam was able to sense supernatural presences in the old Winchester family home, or when he was able to sense Dean's spirit. Under Ruby's training, Sam learned how to use his powers in order to exorcize demons using only his mind.
Sam possesses phenomenal mental strength; as depicted when he overpowered Lucifer, several other supernatural beings, and handled torturous hallucinations that even celestial creatures could not. Sam Winchester is always ready to sacrifice himself for strangers, humankind, and his brother with his every heartbeat sound.
