Ok. so if empress garb is flagged as clothing, is there a reason that it conflicts with draconic resilience? Did some testing and can show drwith basic sorc outfit, and nodr with emp cs. unfortunately cannot upload ss png here, but have them.
It is because of how AC is calculated in 5th Edition D&D and it is correct that Draconic Resilience shouldn't stack with the Empress Garb Chain Shirt.
AC is usually calculated as:
Base AC (10) + Dex modifier + other modifiers
Draconic Resilisnce changes the base AC value, rather than being a +3 modifier. Th formula becomes:
Base AC (13) + Dex modifier + other modifiers
Wearing armor also changes the base AC value rather than being a modifier, so the Garb makes the formula look like so:
Base AC (15) + Dex modifier + other modifiers
Changes to base AC do no stack, so only the highest value should be in use. Draconic Resilience should work with Braces of Deflection though, which is an attunement item that increases AC by 2 when you're not wearing armor. The Garb might work with that too, I haven't tested.
The Garb also works with the Barbarian's Unarmored Defense (even though I wouldn't have allowed that as a DM myself), because it is technically clothing and Unarmored Defense is an "other modifier". So a Barbarian with decent dex and con can use the Garb to get pretty high AC values.