A vehicle power module assembly includes a modular manifold, an upper frame, and a plurality of power stages. The modular manifold includes a first base unit defining an inlet chamber, a second base unit defining an outlet chamber, a mid-unit defining one or more ports open to the chambers, and an upper unit defining a first set of slots and a second set of slots in fluid communication with the chambers via the ports. The plurality of power stages is housed within the frame and each of the power stages are spaced from one another to define inner channels therebetween. The chambers, channels, and ports are arranged with one another such that coolant flowing through the inner channels is in thermal communication with the power stages. The mid-unit may further include flow guides each sized to partially extend into one of the inner channels.