In the US, normal circuits aren't always 20A, especially in residential buildings, where they are more commonly 15A in bedrooms and offices.
That said, if your load is going to be a continuous load drawing 80% of the rated amperage, it really should be a NEMA 5-20 plug and receptacle, the one where one of the prongs is horizontal instead of vertical. Swapping out the receptacle for one that accepts a NEMA 5-20P plug is like $5.
If you are going to actually run such a load on a 20A circuit with multiple receptacles, you will want to make sure you're not plugging anything substantial into any of the other receptacles on that circuit. A couple LED lights are fine. A microwave or kettle, not so much.
This is not true. Standard builds (a majority) still use 15-amp circuits where 20-amp is not required by NEC.