The fuse blowing is most likely because of inrush current, and using a standard fast blow fuse ( common on plastic sealers, which use the same style of construction. They should use a slow blow fuse of 8A, but it is more expensive. 1kVA is common as inrush power, big transformer and low resistance windings. On the plastic sealers the transformer is 56V unloaded, around 2V when heating the strip, though this is incredibly sensitive to the temperature of the sealing strip. I modify the controllers by adding a 100k resistor across the pot outer connections, so that when ( it always will be) turned up to max nuke it is only half the time. 8 seconds of heat is enough to melt a 5mm plastic strip, never mind a 100 micron plastic baggie.