I don't have an Xbox, but just about every system I've poked around in has one. With a system as complicated as the Xbox, I would only imagine there is one around. Lawrence has previously explained picafuses, which are small, resistor like elements that act as one-time fuses. When my SNES died, I poked around and found a blown picafuse to be the culprit. Upon replacement, the system worked fine. It would've been very foolish on Microsoft's part not to include proper protection from surges and the like. But... this is Microsoft we're talking about...