Here is a
link to the FedEx Declared Value and Limits of Liability policy.
As previously stated in this thread, Fedex does not offer insurance. Rather, a shipper must declare a value.
I have read this policy five times, and I have not found any statement about a $500 declared value limit except in the case of a FedEx Envelope or a FedEx Pak, in which case there is a $500 limit. I have not found any declared value restriction related to electronics.
It would seem the difference between insurance and declared value is that insurance would require Fedex to pay the full insured amount, whereas according to the FedEx Policy Statement, a declared value "WILL NOT EXCEED A SHIPMENT'S REPAIR COST, ITS DEPRECIATED VALUE OR ITS REPLACEMENT COST, WHICHEVER IS LESS" (bold emphasis as found in the FedEx Policy).