Are they part of the NCR like the guards and stuff? Because NCR is on their armor and I want to side with the NCR.

also at the HELIOS 1 Power Plant, the NCR attacked me for know reason, is this because the powder gang hates me?

The Powder Gangers were inmates at the NCR Correctional Facility, or NCRCF. They stole the guard armor, and use their inmate clothing as uniforms. They are enemies of the NCR. As to why the NCR would randomly attack you, you might be trespassing, you might have done something to piss them off, or you're just plain bugged.

Also, if you are wearing the NCRCF armor around the NCR they will attack you because they are the enemies of the escaped inmates.

NCRCF?

New California Republic Correctional Facility.

ah, ok. if you havent seen my topic, please check it out, i really need to know who is friends with who in the game

the NCRCF are not friends of the NCR. NCRCF are really the inmates who took over and killed the NCR guards...thus enemies of the NCR. As for who else is friends with the NCR, not sure yet just started the game myself.