At 120v it's what, 1.25A. Not clue what the usual breaker rating in the US is but here they're usually 32A minimum for a ring. Lightning circuits are 6A. A breaker should be designed to carry it's rated load indefinitely at 30 C. May be different for you guys though. As I understand it, every outlet in a US home is on a single spur with it's own breaker, even rated at 5A, that's 600W leaving 450W for the computer.
A high load appliance turning off won't create a higher voltage than what the grid can supply (unless it's a purely inductive load with no supression). What it may do is cause a voltage decrease when powered on due to line resistance.
BTW, I wouldn't trust an electrician that describes an increase of voltage as a surge, that's a spike. A surge is a momentary (or sometimes sustained) drop in voltage caused by a lower impedance path further down the line.