Ok, I know that.
I used VirtualDub a long time, on Windows XP, Windows 8.1, Windows 10 with the same kind of settings of Power Savings. It never went on sleep while encoding.
Now, I use AviDemux. When encoding, CPU is between 20% and 70%, depending encoding parameters. It should be enough to keep alive the computer. But the PC goes to sleep while encoding.
I really think that Avidemux lacks a function to keep alive the PC while encoding, I don't think my settings are wrong.
I you want, I can retry an experience with VirtualDub to be sure.