Dear all ,
Set your proxy in Windows ==> Preferences (General ==> Network Connections)
you have to set your proxy in HTTP/HTTPS only (manual)
if you have still some connexions issues on some your corporate proxies ,
for SPC5STUDIO Marketplace and Update Site,
Contact your "lovely" IT (Proxy or Firewall)
For your information ,
SPC5Studio Marketplace is on the port 9090.
SPC5Studio Update site is on the port 80.