The container running in the intranet with the HTTP proxy to access internet.
When configure the 'Charts Repository Configurations' with the URL 'https://github.com/helm/charts' as the plugin readme instruct, 'connection timeout' showed.
The Jenkins Manage Plugins has the advanced option with HTTP proxy set properly and plugins can be downloaded through that proxy.

Stack trace

javax.servlet.ServletException: rx.exceptions.OnErrorNotImplementedException: connect timed out
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:796)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.MetaClass$5.doDispatch(MetaClass.java:233)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:58)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:876)
at org.kohsuke.stapler.Stapler.invoke(Stapler.java:649)
at org.kohsuke.stapler.Stapler.service(Stapler.java:238)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:812)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1669)
at hudson.util.PluginServletFilter$1.doFilter(PluginServletFilter.java:135)
at hudson.util.PluginServletFilter.doFilter(PluginServletFilter.java:126)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
at hudson.security.csrf.CrumbFilter.doFilter(CrumbFilter.java:80)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:84)
at hudson.security.UnwrapSecurityExceptionFilter.doFilter(UnwrapSecurityExceptionFilter.java:51)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:117)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.providers.anonymous.AnonymousProcessingFilter.doFilter(AnonymousProcessingFilter.java:125)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.rememberme.RememberMeProcessingFilter.doFilter(RememberMeProcessingFilter.java:142)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.ui.AbstractProcessingFilter.doFilter(AbstractProcessingFilter.java:271)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at jenkins.security.BasicHeaderProcessor.doFilter(BasicHeaderProcessor.java:93)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at org.acegisecurity.context.HttpSessionContextIntegrationFilter.doFilter(HttpSessionContextIntegrationFilter.java:249)
at hudson.security.HttpSessionContextIntegrationFilter2.doFilter(HttpSessionContextIntegrationFilter2.java:67)
at hudson.security.ChainedServletFilter$1.doFilter(ChainedServletFilter.java:87)
at hudson.security.ChainedServletFilter.doFilter(ChainedServletFilter.java:76)
at hudson.security.HudsonFilter.doFilter(HudsonFilter.java:171)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
at org.kohsuke.stapler.compression.CompressionFilter.doFilter(CompressionFilter.java:49)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
at hudson.util.CharacterEncodingFilter.doFilter(CharacterEncodingFilter.java:82)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
at org.kohsuke.stapler.DiagnosticThreadNameFilter.doFilter(DiagnosticThreadNameFilter.java:30)
at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652)
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:585)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:553)
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:223)
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1127)
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:515)
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185)
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1061)
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97)
at org.eclipse.jetty.server.Server.handle(Server.java:499)
at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:311)
at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:257)
at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:544)
at winstone.BoundedExecutorService$1.run(BoundedExecutorService.java:77)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
at java.lang.Thread.run(Thread.java:745)
Caused by: rx.exceptions.OnErrorNotImplementedException: connect timed out
at rx.Observable$27.onError(Observable.java:8469)
at rx.observers.SafeSubscriber._onError(SafeSubscriber.java:157)
at rx.observers.SafeSubscriber.onError(SafeSubscriber.java:120)
at rx.internal.operators.OperatorFilter$1.onError(OperatorFilter.java:47)
at rx.internal.operators.OperatorMerge$MergeSubscriber.reportError(OperatorMerge.java:253)
at rx.internal.operators.OperatorMerge$MergeSubscriber.checkTerminate(OperatorMerge.java:797)
at rx.internal.operators.OperatorMerge$MergeSubscriber.emitLoop(OperatorMerge.java:558)
at rx.internal.operators.OperatorMerge$MergeSubscriber.emit(OperatorMerge.java:547)
at rx.internal.operators.OperatorMerge$MergeSubscriber.onError(OperatorMerge.java:263)
at rx.internal.operators.OperatorMap$1.onError(OperatorMap.java:48)
at retrofit2.adapter.rxjava.OperatorMapResponseToBodyOrError$1.onError(OperatorMapResponseToBodyOrError.java:52)
at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$RequestArbiter.request(RxJavaCallAdapterFactory.java:167)
at rx.Subscriber.setProducer(Subscriber.java:211)
at rx.Subscriber.setProducer(Subscriber.java:205)
at rx.Subscriber.setProducer(Subscriber.java:205)
at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$CallOnSubscribe.call(RxJavaCallAdapterFactory.java:141)
at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$CallOnSubscribe.call(RxJavaCallAdapterFactory.java:127)
at rx.Observable$2.call(Observable.java:233)
at rx.Observable$2.call(Observable.java:225)
at rx.Observable$2.call(Observable.java:233)
at rx.Observable$2.call(Observable.java:225)
at rx.Observable$2.call(Observable.java:233)
at rx.Observable$2.call(Observable.java:225)
at rx.Observable$2.call(Observable.java:233)
at rx.Observable$2.call(Observable.java:225)
at rx.Observable.subscribe(Observable.java:8737)
at rx.Observable.subscribe(Observable.java:8704)
at rx.Observable.subscribe(Observable.java:8460)
at com.elasticbox.jenkins.k8s.repositories.api.charts.ChartRepositoryApiImpl.chartNames(ChartRepositoryApiImpl.java:61)
at com.elasticbox.jenkins.k8s.repositories.api.charts.ChartRepositoryApiImpl.chartNames(ChartRepositoryApiImpl.java:48)
at com.elasticbox.jenkins.k8s.plugin.clouds.ChartRepositoryConfig$DescriptorImpl.doTestConnection(ChartRepositoryConfig.java:92)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.kohsuke.stapler.Function$InstanceFunction.invoke(Function.java:324)
at org.kohsuke.stapler.Function.bindAndInvoke(Function.java:167)
at org.kohsuke.stapler.Function.bindAndInvokeAndServeResponse(Function.java:100)
at org.kohsuke.stapler.MetaClass$1.doDispatch(MetaClass.java:124)
at org.kohsuke.stapler.NameBasedDispatcher.dispatch(NameBasedDispatcher.java:58)
at org.kohsuke.stapler.Stapler.tryInvoke(Stapler.java:746)
... 58 more
Caused by: java.net.SocketTimeoutException: connect timed out
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:350)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:206)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:188)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at okhttp3.internal.Platform.connectSocket(Platform.java:126)
at okhttp3.internal.io.RealConnection.connectSocket(RealConnection.java:140)
at okhttp3.internal.io.RealConnection.connect(RealConnection.java:111)
at okhttp3.internal.http.StreamAllocation.findConnection(StreamAllocation.java:188)
at okhttp3.internal.http.StreamAllocation.findHealthyConnection(StreamAllocation.java:127)
at okhttp3.internal.http.StreamAllocation.newStream(StreamAllocation.java:97)
at okhttp3.internal.http.HttpEngine.connect(HttpEngine.java:289)
at okhttp3.internal.http.HttpEngine.sendRequest(HttpEngine.java:241)
at okhttp3.RealCall.getResponse(RealCall.java:240)
at okhttp3.RealCall$ApplicationInterceptorChain.proceed(RealCall.java:198)
at okhttp3.RealCall.getResponseWithInterceptorChain(RealCall.java:160)
at okhttp3.RealCall.execute(RealCall.java:57)
at retrofit2.OkHttpCall.execute(OkHttpCall.java:174)
at retrofit2.adapter.rxjava.RxJavaCallAdapterFactory$RequestArbiter.request(RxJavaCallAdapterFactory.java:160)
... 87 more