You can use a "delay on break" relay. They're widely available (Amazon) and inexpensive at $10-15. You connect your load to the relay and if power is cut there is an adjustable delay to turn it back on. The issue is they won't handle much of a load at all. Most of them are only rated for 1 to 1.5 amps. You would have to wire one up to control a relay that would control your load. So at a minimum you need the delay on break relay, a load relay, a normally closed momentary switch, some kind of box to mount it in, an outlet to control and a power cord. You wire the delay relay the momentary switch and the coil of the load relay in series. The contacts of the load relay normally open terminals are connected to the electrical outlet. Normally you will have power running through the switch through the delay relay and energizing the load relay coil and powering the outlet. Push the button to interrupt power and the both relays open and the outlet turns off. When you release the button power is restored to the delay relay and after the delay time it will switch and allow power back to energize your load relay and restore power to the outlet.