If Ko-Tun has Self-sufficient and Power Charger could they both trigger off of one token? i.e. declare an attack, spend one damage power token for +4 to the attack (+2 from each card).

I would say no, because both specify explicitly "+2 of the symbol instead of +1". Thus they are not additive.

Self-Sufficient applies +2 instead of +1, but either Power Charger sees +2 and doesn't trigger, or still only applies 2 of the symbol.

If the wording were "apply additional symbol according to the power token type", they would be additive.

That wording made me question it. A bit of a stretch thematically as well.

Just my opinion, but I don't know of any ruling to the contrary.

IMO You can use both effects if you want to (they are two different effects with the same trigger) but - as A1bert said - they are not cummulative, so one of the effects will be wasted. For me, the wording is clear - both effects change +1 to +2, so when You trigger first effect You will change +1 to +2 and there is no longer +1, that can be changed to +2 by the second effect.