Will my line 6 spider 3's power cable work with an engl screamer, or would it damage it in any way?
If it's an IEC type, it should work fine. IEC plugs are the 3-prong female types that plug into equipment, such as amplfiers, computers and other equipment. It's a standard type of connector.

If you need to see a picture of an IEC connector, just let me know.
Theyre the same type of cable, its just my engl one only came with an american plug, and i dont want to travel the 3/4 of an hour back to the shop. =P
The Engl came with an American cable? Did you make sure the amp is set up for 240 volt too? Cause 240 volt into an American 120 volt amp would be a spectacular "bang"
It says 230V on the back on the amp, so im hoping it will be ok.
Okay.... 230V is a new variable. I think I'd want to ohm out the line and make sure everything is the same. It should be, but I don't have the exact answer on that one. If I were at work right now, I could ring out a 230V IEC connector and verify that, but I'm at home and have no way of ohming one out. Most likely they're wired the same, but if not... it could be interesting.