Unfortunately, the warranty does not cover the power supply, so if you have a power supply that isn't working, you can just throw it away and purchase a new one. You don't need to find a charger that is specifically designed for Chromebooks; any charger that has a USB-C connector and has a power output of 15 volts and 2 amps will work. Many chargers will support a range of outputs - as long as 15 volts and 2 amps is within its output range, it will work fine. When you see a product listing for a power supply, it might indicate 30 Watts or 45 Watts (remember Watts = Volts * Amps) and they will typically advertise the maximum wattage. You should be able to find them for about $20 to $30 each.