For these reasons, an internal load is often added to the power supply to prevent these problems. When an external load can be depended on to provide a minimum load, this internal load can be removed resulting in higher efficiency and more load capability. Hence, some power supplies do depend on an external load being present for proper operation. This is apparently what is happening in your case . Others may have a different perspective on this topic.
Comments are always welcome.
The output is tightly regulated, and the current is bounded, but the duty cycle is chaotic. And then the self-powered controller which cannot generate enough bias from an auxiliary winding to keep the bootstrap off. It either burns up the bootstrap device, or cycles on and off. Ray Ridley, Ridley Engineering , is a sponsor of this website. More about chaos .