In reply to indrajeetpande:
The function $sformatf() is in the SystemVerilog LRM and its functionality is fully defined.
The function $psprintf() IS NOT in the SystemVerilog LRM, and there is no clear definition on how it should function. However, it is a legacy function that most simulators support since removing it would break a lot of code. You should not use this as you are relying on implicit support by simulators.