Laptop failure due to constant fluctuation of AC frequency and voltage
Don't worry. Your PSU doesn't really work with AC. 

Most modern PSU fist change the AC to DC via a rectifier. The internal electronic then creates an own AC used to transform the voltage to the desired one. The internal AC has a much higher frequence to be more effecient.

Most PSUs work with frequencies from 0 to over 60Hz. Even DC with down to 80V is possible. So anything up to 60 Hz should be fine, if you have between 100V and 240V.