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Recently I played a game in which my opponent(chaos space marines) had five terminators that were equipped with various weapons.
They had assaulted my deff dread and some of the terminators were using power weapons. I was wonder if regular power weapons were conferred a bonus such as double their strength or something along the lines of that. I thought that it was pretty weird how although the terminator's power weapons are able to cut through armor like butter, they would not be able to cut through the front armor of my deff dread. When I looked through the rulebook, I could find no such evidence.

Please clarify this predicament for me!

with a regular PF its a S(2x x being the S) I1 attack, but with chainfists its like throwing a melta bomb, as you roll 2d6 for penetration, with the regular PF rules.

There is no such rule unless you specifically use power fists or something similar. Regular power weapons only ignore armor saves.

throwing a melta bomb, as you roll 2d6 for penetration

I believe Melta bombs are not melta weapons, so they only get 1d6 armor pen rolls

But no, regular power weapons have no special effect on vehicles

*EDIT* My bad, hang on, Its AP1 they dont have, pretty sure they do have 2d6 pen whoops

You believe wrong; and Kinda right at the same time.

They are not "Melta weapons" because Melta is a shooting rule and requires you to be within Half the weapons maximum Range to gain the Extra d6.

Melta Bombs are grenades, and as such a Close combat "weapon" with no range(other than base-to-base, or within 2" of a model that is in Base-to-base) so there is no capability to be within half range(unless you are dividing 0 by 2). Melta bombs are Grenades with their own special rules and one of those rules is that you roll 2d6 for Armor penetration.

And after typing all that I just read your edit; I am still posting this but now you can apply the Meltabombs are not shooting attacks to why they are not AP1.

To clarify, Meltabombs are not AP1 because, as said, they are not a shooting attack.

Power Weapons do not have any bonuses against vehicles.