[RPG] Do Power Sources really matter

Nope

Unless it specifically says otherwise they do not stack. It's item 28 on the PHB FAQ over at Wizards.com.

Note that this applies to all resistances, so you'd only get the Resist 10 All.

Edit:

Here's a snippet from the Compendium entry that is linked in the FAQ.

Not Cumulative: Resistances against the same damage type are not cumulative. Only the highest resistance applies. For example, if you have resist 5 cold and then gain resist 10 cold, you have resist 10 cold, not resist 15 cold. Similarly, if you have resist 5 cold and then gain resist 2 to all damage, you still have resist 5 cold, not resist 7 cold.

The canonical "true/current" version of everything is found in the compendium, here (subscription required to use as more than an index).

There are, at present, three current "Cleric" classes you can play. I define a cleric class as anything that counts as a cleric for purposes of feats, beyond that of multi-class.

There is the "original" Templar Cleric. Recently renamed from "Cleric", the templar cleric is the cleric of healer's lore, lasers, and optional pacifism. A number of its powers have been errataed to reflect appropriate range and power. (Otherwise it was a rather superior controller.) The most important errata is the limitation on buffs to surgeless healing, and is the only critical errata to apply. (Basically the rule of thumb is: if you don't pay a surge for it, it doesn't get buffed by anything)

There is the essentials Warpriest. The warpriest is a simplified melee cleric featured in the essentials books. It uses domains and features the current domains of death, earth, storm, and sun. Death is debuffy, Earth is forced movement, storm is buffing, and sun is glowy (that's a shocker right there...) I am not aware of any major errata that must be applied to the class to correct game-breaking brokeneness. The warpriest shares few mechanics with the Templar, and should be considered a different class that shares feats, general role, and PPs.

There is the PH3 Hybrid Cleric that stinks. Avoid it. But it's there. There are no major updates for the hybrid cleric.

Sources of truth

The most important source is DDI. The second most is the Rules Updates. Everything that appears in a book is compiled and/or changed in those two. DDI is more authoritative than the rules updates because sometimes wizards engages in "stealth nerfs" (see Divine Oracle) that aren't loudly announced and may or may not be reflected in the rules updates.