Nowadays, many property power supply systems are reluctant to be handed over to the electric power bureau. Is it illegal?

It's not illegal. Developers don't pay the power supply company supporting fees, but pay their own money to build low-standard power facilities. After handing over the house, they don't want to take care of it, and then they want to hand it over to the power supply company. If they pass the acceptance, the power supply company will generally accept it. However, if the power supply company fails to pass the acceptance, it will definitely not be accepted. The cost of later reconstruction is too high for the State Grid to invest. If it is not handed over to the power supply company, it can only be managed by the property in the later period, and the electricity price is bound to be high, and the maintenance and transformation in the later period can't keep up. It won't take many years for transformers and lines to go wrong, and low voltage and frequent power outages are indispensable.