This paper presents the design and implementation of a universal Multi-Input Multi-Output (MIMO) power converter with many Linear Extendable Group Operated (LEGO) building blocks, namely LEGO-MIMO architecture. The LEGO-MIMO architecture can be used to synthesize a wide range of power converters with universal input and output range. In a LEGO-MIMO design, multiple dc-ac units are coupled together through a multi-winding transformer. Each dc-ac unit can individually regulate its port voltage and power. Many dc-ac units can be connected in series or parallel to meet the targeted voltage or current ratings. The modular units can be designed and manufactured in large volume with low cost. This paper studied the design methods for the multi-winding transformer. We also investigated the strategy to control the sophisticated power flow in the multi-winding transformer and proposed a matrix model for the LEGO-MIMO converter with reduced order to simplify the control algorithm. A LEGO-MIMO prototype with 12 LEGO bricks and a 12-winding transformer has been built and tested to verify the effectiveness of the proposed LEGO-MIMO architecture.