Generally speaking, Model Power's freight cars are Chinese-made copies of older cars originally designed and manufactured by Roco, Lima, Rivarossi, et al. I'm told that tooling for these knock-offs gets tweaked on a fairly regular basis, resulting in many slightly different variants.
This model appears to be a copy of the old Atlas (USA) 40' PS1 box car. One of the most successful freight car designs of all time, over 76,000 PS-1s were built by Pullman-Standard between 1947 and 1968.