I've found that it varies. For example, with 30A adapters, there are cheapies which burn out and get hot, but then there are the larger Camco ones (as well as their dogbones) which work well for a long time.
Some products, marine-grade is the only way to go. Especially when it comes to plumbing an electrical work. Costs more, but for items where the labor can mean many man-hours to get to the problem, it is worth it.
All and all product quality as a whole has suffered. I can compare tools from the '80s versus wrenches made now, and the differences are obvious. For tools which were "average" a few decades ago in quality, I'd have to buy MAC or Snap-on today to get the same fit/finish/material work.
Where Sears went wrong was losing their good name and offshoring. Once their products went from top tier US made goods to just another brand off the Chinese slowboat, people just went with cheaper stuff that was at the same quality tier, such as Home Depot or Lowe's house brands, or even the Harbor Freight specials.
Had Sears actually stayed with their "Sears Roebuck & Co." quality name and avoided the mass migration of good making to China, they might be still relevant today.