Kim Jong Un's visit to China hasn't affected US interests too deeply. The entire point of the secret meeting was to mend whatever relations had been previously damaged and to get China back on North Korea's side. North Korea needs a financial powerhouse like China when dealing with the US because the United States is known to be a tough negotiator.
The other problem is the fact that the visit was secret and because there is such a long-standing history between North Korea and China, it may have renewed ties between the two countries. This affects American interests because China could potentially play into exactly what North Korea wants instead of cooperating on deals that would benefit us.