Can SMPS works as cellphone charger?
1) The phone determines the charging rate, so not the power adapter.

2) The original power adapter uses signals (on the USB datalines) so that the phone knows it is the original power adapter which can deliver the required current.

3) the phone cannot detect that the SMPS can actually deliver 2A (since the SMPS does not provide the identification signals like the original power adapter does) so the phone plays it safe and draws a smaller current. Then charging takes longer.

It depends on the actual charger and phone model what will be needed to make the phone fast charge with a non-original adapter. For some (older) devices shorting the DATA+ and DATA- pins is enough. Others use more complex signals, like QuickCharge.