Verified with Adamantine Cloak of the Dragon and Stormreaver's Tablecloth (tier 1):

Pre-U19:
"Spell Focus Mastery +2: All spells have the DC to resist their effects increased by +2. This bonus does not stack with other item-based spell focus effects."

U19:
"Spell Focus II: Passive: +2 Equipment Bonus to the DC to resist all of your spells."

Note that Turbine explicitly removed the phrase "This bonus does not stack with other item based spell-focus effects."

It's about time that spellcasters got a the same treatment as melee who have long benefited from Combat Mastery and a specific tactics bonus (such as Stunning +10) stacking with each other.

With Twilight equipped, I verified that I gained +2 DC to Blade Barrier when equipping the cloak.

Old news.  Kookie kobold said something along the lines of it "probably" not being WAI.  While the non stacking phrase was removed, it's almost assuredly (IMO) just due to automatic  text conversion of old properties - note that the "mastery" part was also removed to differentiate between standard focus e.g. evocation focus. 

So unless +5 evocation focus stacks with +3 evocation focus, or unless stated explicitly to be WAI, I wouldn't build for it as it seems subject to be patched.

https://www.ddo.com/sites/default/files/GlovesoftheMasterIllusionist.png
+x Equipment Bonus to the DC to resist your Illusion spells.

Does not seem WAI