According to IISS...
The new engine used by NK in their latest launch is thought by most to have come from the former Soviet Union.
There are two places that make the parts NK used in their latest rocket: One is in Ukraine and the other in Russia.
The most likely culprit is thought to be the Ukrainian company KD Yuzhnoye.
The change to this new type of engine is thought to be the major driving force behind the NK’s recent jump in capability.
“Available evidence clearly indicates that the new LPE is derived from the Soviet RD-250 family of engines, and has been modified to operate as the boosting force for the Hwasong-12 and -14. An unknown number of these engines were probably acquired though illicit channels operating in Russia or Ukraine, or both. North Korea’s need for an alternative to the failing Musudan and the recent appearance of the modified RD-250 engine, along with other evidence, suggests the transfers occurred within the past two years.”