This mod requires Paramonov95's REL v3 and Rilissimo's REL generator to function.
Why REL ? Technically it can be run with the generator alone, but it can't delete pre-generated items from containers in vanilla or in the integrated mods, and REL does that
Why generator ? The mod requires data only the generator can output at the time you press the 'Generate' button, it will not work without.

Note that it doesn't alter REL's treasuretable drop chance of any item/container. So using REL with or without REL_SE is essentially the same in functionality. What it does is to take half (by default) of all the items from REL and inject 1 (or none) of them into:
+Traders, when you ask them to trade, once per long rest
+Non-empty bosses and chests for the first time when you loot them, regardless of ownership.
For looting chests, the mod only triggers when you manually open them (unless you have Auto Loot and enable the optional feature related to it), which means if you destroy one then you'll get nothing beyond what already exist in the chest. This means you can open a chest, get a loot (or not), then reload to a point before opening the chest to try for another item. Due to the total number of items, it is unlikely that you get the same one twice before and after reloading.
*Also, with REL_SE you can randomize cosmetic items in the generator. This must be set manually, and meant to be for camp clothes, shoes and underwear, like Scantily Camp Outfit. Items flagged as Cosmetic are not removed from the pool once dispensed. This means if you assign a unique item to Cosmetic category, it can be obtained over and over again from REL_SE.
* The script treats rolling for cosmetic items independent of unique item. That is: if you fail to roll for a chance to get a unique item, you still have a chance going for a cosmetic item, or vice versa. You get 2 items, 1 unique, 1 cosmetic if you succeed in both.

Since the mod uses handle ids for chests in the script, it will work with any other localisation, not just English. Note that statuses exclusive to this mod is only in English, however.
The mod will print out lines into the script extender console if it finds a chest matching its handle id record. So if you feel a chest or types of containers should be added, inform me of its name and location.

The only 3 categories REL_SE affects are: chests, traders, and bosses, quest rewards are handled by REL exclusively

You could go 100% on REL_SE using the scaling option of the generator, this hypothetically would have REL distributing only its builtin items (~600 equipments) plus modded items that are inserted to the tutorial chest (except for those you mark in the generator to appear in that chest), so most of the time and depending on integrated mods, chests initially will give you 2 items, 1 from REL, 1 from REL_SE, then drop to 1 from REL_SE only as REL runs out of items. (maybe some time in Act 3, because it's going to take a while to deplete 3 digits amount of stuff.)
For 100% REL,  REL_SE only handle items marked as cosmetic, manually by the user.
* These settings are done via Rilissimo's One-Click generator, REL and REL_SE do not interact with each other beyond the point of generation.