My laptop USB port is outputting 5.8 V. Is this in tolerance?
The USB specification says 4.4 V or 4.45 V to 5.25 V for VBus. Some non-standard USB supplies will be higher to combat the voltage drop over a long wire and high current, but it is not within normal specifications.
Are you measuring under load? That would be important. Most devices will regulate down and even 5 V ICs tend to tolerate up to 6 V, so it's not a great problem.