If multiple items have the same enchantment, does the bonus stack?

Certain enchantments can be applied to multiple items, such as both an amulet and a ring. If I wear two items that grant the same bonus, does the bonus stack? (e.g. if I wear an amulet of +12% Alchemy and a ring of +12% Alchemy, do I get +24% to Alchemy?)

Also, do some enchantments stack while others don't?

Solution 1:

Instances of Fortify X (Where X is "Conjuration, Smithing, One-handed, etc.") stack if they're from separate items.

You cannot use the "Double Enchantment" perk in the enchanting tree to double-enchant a single item with the same enchantment, twice.

Unlike in Oblivion, stacking skills above 100 actually increases their effectiveness.

Solution 2:

I can confirm that +carry weight, fortify alteration/destruction, better prices, +health, and +mana all stack. I have boots and gloves of +37 (I think) carry weight, and they stack additively to 374 total (from 300 base), and stack with my Voldun mask which adds another 20. Fortify alteration/destruction are additive, so four 25% mana reduction enchants stack to 100%, or zero mana cost. Voldun mask reduces prices, then equipping the Amulet of Zenithar reduces prices again, though I haven't checked to confirm it's additive (i.e., it should be 20% + 15% [I think] is a 35% reduction, which is close, but I haven't confirmed it). +health and +mana stack additively.

I know +weapon skill enchants stack, but I haven't really played with them. I believe they stack additively, then the combined percent is compared to the weapon damage. So if you have an improved weapon with perks and stuff, and it's sitting at 50 damage at a skill level of 75, then you get four +20% weapon skill enchants, they would add to +80%, and 75 + (80% * 75) = 180% * 75 = 135. Then, your actual damage would be measured as though you had a weapon skill of 135. As far as I can tell, skills scale linearly, so your final damage would be 180% * 50 = 90 (if this is true, you can just calculate +weapon skill enchants as though they are +weapon damage enchants).

Solution 3:

Smithing stacks, but it does not fortify your smithing level, only the upgrade value of armor or weapon.