You could use a mains transformer, say 120V primary, 10V secondary. Then use a bridge rectifier and large smoothing capacitor. This will give a fairly large amount of ripple at 100Hz / 120Hz, depending on your local mains frequency. Depending on the application, if you need better smoothing, a low drop-out regulator could be used. This will be the simplest solution. Don’t try making a direct off-line switched mode supply.. You could use a simple switched mode supply after the mains transformer to get the smoothing at a higher efficiency.