If you applied for the patent of Ningbo Wansheng energy production in China, you may have obtained permission from the patentee. Of course, Wansheng also has to pay the patentee's patent fee.
Small factories in China produce for two reasons.
1 China people are best at making counterfeit products without the permission of the patentee.
In China, it is legal for anyone to produce and use them without applying for a patent.