Who are they -- the North Korean new rich? The upper crust of this social group consists of high-level officials. Some of them have gained their wealth through illegal means, but many have seen their business activities permitted and even actively encouraged by the government. Most of the money is made in foreign trade, with China being by the far the most significant partner.
Surprisingly, many people in the countryside still buy fridges, even though the contraptions are unusable most of the time. I have frequently come across North Koreans who have boasted of the fridge they own, only to admit that they do not have electricity to switch it on. To my perplexed question of why they spent so much money on such a useless device, my interlocutors would usually reply that a fridge was an important and even useful status symbol. An affluent household nowadays is expected to own a fridge, even if it is used as a bookshelf (as was the case with one of my North Korean acquaintances).