Your experience aligns closely with mine. Our products were industrial systems designed for applications like power plant consoles and remote generators, adhering to UL 508 specifications for electrical panels, including dials, gauges, switches, and industrial computers.
Due to our size, we lacked the ability to self-certify and had to send our products to UL for first-article certification. Subsequently, quarterly factory inspections ensured consistent adherence to standards.
Our certification was essential due to UL’s establishment of a ecosystem of 508-certified panel builders, crucial for industries like pharmaceuticals and breweries. This certification acted much like Apple’s MFI(made for iPhone) cert in that you needed this “badge” if you wanted to play in that market. They even gave out plaques to hang in your lobby to show you were 508 certified and you were authorized to use it in your marketing material.
Our CEO harbored deep resentment toward UL, dubbing them the “Chicago Mafia” for their extortionary tactics, such as switching standards and imposing exorbitant certification costs. With a stroke of a pen, they nullified all of our certs when they switched to ISO and made us go through certification for everything. That was a $300K bill if we wanted to do this and we were only a $6million company. We were forced to obsolete nearly half our product portfolio.
I bring this up because there no doubt will be someone in this forum who will point out that Bambulab uses a Meanwell Power supply that has many agency certs. Not so fast. that is a “UL Recognized” [u[component[/u] and does not matter at all for a consumer product.
For UL at least, my compliance engineer told me that anything that uses wall current and marketed to a consumer, must have a UL cert. For medical devices, there was a different cert and that was for any product that came into direct contact with a patience. If memory serves, the threshold was 48V which incidentally is what the US telephone system operates off of.
I can tell you from personal experience that it is not exactly true. I had one customer—a UL 508 certified panel shop—that decided to use a cheap Chinese knockoff of my product. It was a panel computer and had a UL sticker. They paid dearly for that mistake.
My customer made multimillion-dollar power substations, and they had just shipped $12 million worth of product to Chicago O’Hare airport—Chicago being the hometown of UL. We’re talking 11 flatbed tractor trailer’s worth of bulky equipment. When it came time to sign off on the safety inspection, the inspector didn’t even bother to inspect the $12 million dollar system; he went straight to the Panel PC and said, ‘Pull the file on that…’ When they did, he pointed out that the product was UL certified for office equipment and not UL 508.
That story didn’t end well for that customer. Since their product was already in the field, it could no longer be self-certified under 508… oh no… they had to pay an extra $60K to get it field-certified. You see, that’s a different UL department. 
The point being is that many large US cities like Chicago, NY, Boston, DC, Philly, and such have very strong industrial safety standards that one needs to comply with. It’s one of the many reasons we don’t see large factories like we saw in Detroit anymore, along with the cost of doing business in a big city. But it’s a lot easier to get a plant certified in Podunk, Mississippi, than in the Chicagoland area.
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Just as a side note for those folks who don’t know the history of UL: ‘Underwriters Laboratory’ was founded in 1894 as a direct result of too many electrical fires stemming from what was then a new technology: electricity. ‘Insurance underwriters’ quickly endorsed the not-for-profit entity to certify electrical products. UL was a customer of mine back in the day and I recall that they ran more like a public utility than a company. They told me that there was a brief period where an insurance company could deny a claim for a structure fire caused by a faulty device if it did not have a UL certification. Of course that’s no longer true but that can shift liability of a fire back to the manufacturer.
When municipalities and governments around the world, including in the US, started to accept other certifications such as Germany’s TUV, the competition caused UL to reorganize in 2012 as a for-profit entity. That was right around the time I was involved with 508 products and UL morphed into a money-grubbing parasitic monster.
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