The OEM's for ASUS' power supplies are AcBel Polytech, Bestec, Delta Electronics and Enertronix.
The OEM's for Gigabytes power supplies are AcBel Polytech, CWT and FSP.
The quality of components varies depending on the model series. In general a value series will use cheaper, less reliable components in its manufacturing. High-end series will use high quality components and are better able to deliver their claimed wattage or more.
If you specify the makes and models available to you that will be more useful in helping you make your decision.