The last few things I got in from Kipper has Sullins printed on them. If you can get a sample from a Chinese or Taiwanese company I say go for it, but if your looking at only getting say 100 at a time and they offer you them at under $10 each, no way are they going to be good quality.
It is totally random what the build quality of any supplier is. It depends on their production method and attention to perfecting a production run.
What you need is an unbiased quality control of sample assessment.
Cost is an indicator of quality, but the real proof is measurement. How thick is the gold plate? How consistent is the build? How reliable are the tolerances? Cost isn't just based on raw material cost. Some outfits in that part of the world make with recycled ingredients. If you effectively have your own gold mine for the plating process, that helps enormously. Likewise, recycling ABS for the plastic carrier. You can cut unit costs to the bone that way. In a lot of courntries you even qualify for a government subsidy because you are earning them carbon credits. Claiming it can be very awkward though.
It's a jungle, the supply chain. I'll agree with you there.
But, if you get a manufacturer with spare capacity of a LARGER, longer adaptor size, that can be cut down precisely, that is one way around. Likewise, adapting two smaller adaptors.
You got to be flexible in what you can use, but absolutely cast iron with regards to what you accept as quality stock. I'm right with you on that last point, Chief.
Finding perfect with one supplier is unlikely. You might end up buying two smaller units from different suppliers. That would mean checking BOTH for build quality and tolerances. It sounds easier but it still has issues that you have to address and get the right answers to get a reliable, dependable circuit.
And of course, if the free samples are a bit skimpy on the gold plate, you can always try extra plating them. You won't save every single one probably, but that can be worth doing too. Just don't overdo it, it's a very subtle process to manage properly. That's what Sullins are really charging for - consistency of plate.