Did the yellow-eyed-demon's blood give Sam his powers or did Sam already have powers?

No he didnt already have powers, when he was 6 months old the YED dripped his blood into Sams mouth and then when Sam was older he started drinking demon blood mainly Rubys to help him get more powerful in order to kill Lilith, hope this helps :)

I think maybe he already had them, and the demon blood just kicked them in gear. It's just like he already had the powers, he didn't need Ruby's blood to make them stronger. He just needed to practice using them. Ruby had him by the short and curlies the whole time.

It was the demon blood that gave Sam his powers, like the rest of the "special kids". The best reference I could find is in 4x3, "In the Beginning", where the YED is possessing Samuel and he says to Dean: "Demon blood is better than Ovaltine, vitamins, minerals - it makes you big and strong." :))

The yellow-eyed demon Azazel dripped demon blood into Sam's mouth when he was 6mnths old when his mom died. The 2nd last episode of Series 2 covers this if ur not sure :)