Do power weapons, power fists, ect. affect just one attack of the equipped model (IE a Marine with three attacks and a power weapon gets two normal attacks and one power weapon attack) or are all attacks affected (IE the same Marine has three power weapon attacks and zero normal attacks {Assuming the controlling player chooses to use the power weapon- that I managed to see in the Special Close Combat Attacks section

})?
My friends and I have been working off of my interpretation of the rules for quite some time now, which of course I learned myself from reading the manual.