2 answers here:
1) L3+ draw is about 750W, so at 120V that's approx 6.5 A, so there is absolutely no problem drawing that from a standard 120V 15A outlet.
2) To be "SAFE", consider that the PSU can draw up to 1680W, which at 120V is 14A. That's right at the limit of the available power from a standard 120V 15V outlet. Consider that most PSU's are rated around 80%, so if you divide 14A by 0.80, you get 17.5A which is overloaded for that circuit.

So, a single L3+ is fine on a 120V 15A circuit, The wattage of the PSU is a max rating, doesn't mean it will actually draw 1680W if the load is only 750W then it will draw 750W and not 1680W.
You could have a 10000W PSU and if the "load" on the PSU is 750W then that's what you will see at the wall outlet (don't forget the 80%, so more like 925W max). Still well within a single standard US circuit limit.