For relay circuits, I prefer solid-state relays that buffer the input. No large in-rush current or large reverse-voltage spike to mess with (or destroy) the driving circuit. SS relays come in two general flavors; a buffer before a conventional relay, meaning you still have to supply coil power from somewhere, or ones that use FET switches instead of a mechanical relay. For ether flavor you still need a 12 V line someplace; I've used a cheap wall wart.
I forgot about the little USB-12V converters; seems an easy solution.
I forgot about the little USB-12V converters; seems an easy solution.