For almost all devices we use power supplies which transform AC into DC, adapted specifically to the power needs of the device.
This 9 pages in depth post about power and power supplies has been travelling all over internet. Jon Chandler specifically speaks about Wall Warts, the ones who transfer AC to DC.
His article was featured on Hackaday and Makezine – but I thought that for future reference it’s nice to write a little about it on Ellentriek.

Important stuff!