Original Acer Chromebook CB515 ac adapters are listed below, simply select your model and it will display the full specification of the power adapter needed, 2 different power ratings are available, so if unsure simply select the 65w as this fit all however,  the Acer CB515-1W although compatible with 65w USB-C, was originally supplied with the 45w version, whereas the Acer plus CB515-2H does need the 65w, with both available below and supplied with both charging unit and power cord.