Outside of paintball 'white box', is unbranded / generic
It could be 'oem' items such as in IT without manuals, software, warranty etc. Intended for sale to a pc builder, tech support etc, the buyer gets there warranty from the pc builder or a company has their own support staff etc
These are cheaper because the manufacturer don't carry the costs of support, and could have less features or be the end of line after an upgrade to the next version
It could be from a dodgy Chinese factory that are subcontracted by a brand and make more to sell on themselves - or the quality control rejects
White box could be manufactured by a brand and sold for rental paint without exposing the brand / use as an 'own brand'
It could also be reject paint and sold cheaply under plain boxes to reduce loss