Here's how you convert watts to amps.
There is an equation. P=I * V.
Power(P) = Current(I) multiplied by Voltage(V). So move the equation around and you get.
I = P/V (current = Power divided by Voltage)
So, your 12volt 1.5 Watt charger produces 0.125 amps and the 5 Watt charger gives you 0.417 amps.