A power plan is a group of settings that manages your computer power usages. You can use the feature to customize the amount of power being use, performance increases or balance them. Anyway, what if your computer still sleeps even if you set that into the Never feature?
Let's go the the power options and see other customization that can be use.
Quick tip: if you can't find the settings at your taskbar, type "powercfg.cpl" to your Run window or command prompt.
To customize the Balanced power plan, In which, as shown it automatically balances performance with energy consumption on capable hardware.
Double-check if the computer is set not to sleep at plugin and go to "advanced power option" to see other features of the plan.