I have an old Dell 250watt DC power supply, and I quickly need a 24 VOLT AC ~60Hz Output PSU for a device that consumes 5 Watts. Is there any easy, safe way convert my PSU to so this? By the way, we get 120 VAC ~60Hz house-current here. Thanks.
Easy & safe? Nope. Computer PSUs are designed for DC output, not AC.
Try a local home-improvement or hardware store. Thermostat or doorbell transformers often put out 24 VAC, and will supply more than enough current for a 5-watt device.