Most Protestants will proclaim that they believe in ‘scripture alone, but most believers don’t apply this to their lives. And most will add or take away a little here and there.
Calvinists, 
who loudly proclaim: “Scripture Alone!,” not only don’t practice it, but actually teach many things outside of scripture.
For example, they will tell you that God has to do something outside of scripture for someone to be able to have faith. God has to give you that faith. They have come up with extra-Biblical terms to form their theology. Depravity isn’t in the Word of God, let alone Total Depravity. Election is scriptural, but unconditional election is not, nor is there any “limited” atonement to be found. Grace is there, but it isn’t irresistible. And their perseverance of the saints theology is heresy.
The idea that regeneration precedes faith is ludicrous when one considers Romans 4:3 For what saith the scripture? Abraham believed God, and it was counted unto him for righteousness.
The final question is: Can ‘the man of God be perfect, throughly furnished to all good works’ by scripture alone?