Disclosed is a power system that may be housed inside a single ISO shipping container having standard outside dimensions. The system may include a power source and an internally integrated aftertreatment module that is removable as a unit and that comprises, for example, Particle Filters (PF), and/or Oxidation Catalysts (OC), and/or Selective Catalytic Reduction (SCR) systems. The power system may include other removable modules such as a power module comprising a generator, pump, chipper, chiller, or other power equipment, a container module for fuel, and a container module for reductant, both of which may be non-rectangular in cross-section. A system is also disclosed for providing on-site power in the absence of shore power.