Assessing economic developments in North Korea is extremely difficult. The country has not published any regular national account statistics since the 1960s or any budget information since the early 1980s. Almost all the Korean, English, French, and German literature on the matter is extremely anti DPRK biased (for obvious reasons). I'd send you a Chinese paper but you can't read Chinese. Here is one of the less biased, recent, English pieces as a starting point. In it you'll find a more vibrant economy than you want to believe: 

here's a start:
https://one.oecd.org/document/ECO/WKP%282020%2915/En/pdf 

 Well, presumably their welfare is at the level of Cambodia.