“Unplug your devices when not in use” sounds annoying, but it’s true. The trick is knowing what matters most. What is vampire power? Also called phantom load, it’s the electricity devices use while “off” or idle—anything with a clock, light, remote, or sleep mode. Common culprits: Cable box/DVR: 20–30 W Game console (rest mode): 10–15 W Desktop (sleep): 5–21 W...