It really depends on the type of Computer systems you may have. It will not increase performance rather allow your components to work properly without dying.
By the way you posted in the wrong location.
i'd say they use average quality psu's. All system builders , dell, hp, acer use average components, in acers case less than average. They make a bigger profit that way. You cant compare them to more well known brands like Antec, corsair etc.
i use a dell vostro 200 slim. ithink its bestec 250watts