Translation:This computer is powerful, efficient and simple to use.
But effective (efficacious) is also a common, if not more common translation. I looked up collocations and found it translated as effective and efficient about the same number of times. I found this one: "gestion efficace du portefeuille n. efficient portfolio management" and, frankly, I would prefer effective portfolio management! Effective and efficient are very different in English, but not in French.
Im sorry but absolute no one would describe a computer as being efficacious. I doubt they would even say effective without at least adding context. That computer makes an effective doorstop for example. By the way, has anyone heard the lyrics to "Lily the Pink"? Efficacious used in song.......
"This computer is powerful efficient and simple to use"
...it never breaks or crashes while you are typing a letter and loses the entire thing, the updates only happen when you are not looking and install in an instant anyway, it plays every game ever invented for the platform without any compatibility issues on the old ones there is no gunk under the keys and the screen just stays permanently clean on its own, it makes no persistent whirring noise that gets on your nerves after the first hour, it does not get hot and everything you plug in will just work instantly without a driver install or any other issues, all the software you ever paid for to use on it will last for ever and you will not get eye strain or repetitive strain injury from using it, no known viruses have been written for it.
And yesterday I left it on the bus. ahahahaha ...very old joke.