Is it safe to replace a capacitor that is rated at 3.8uF/300V X 5uF/250V X 6uF/250V with another that is 4.8uF/280V X 6uF/250V X 6uf/250V? I ordered a replacement and this is what the company sent to me to use.

Yes. As long as the capacitance is as least as large as the original. The fan is 120 volt so no problem there. Tolerances on these devices are routinely +/- 20%, for high quality caps, so go figure.

John, I disagree in part.

Too large can cause the motor to overheat.

Too small will cause the fan to run slow.

However the cap they sent you should be fine. I usually go by +/- 1uf.

Ceiling Fan Capactors - Troubleshooting and Resources - Ceiling Fans 'N More