What current is safe for Wemos d1?
With very few exceptions, electronic devices only draw as much current as they need, limited by their resistance. 

The current rating on a power supply is the MAX current it can provide before the voltage drops. Having a higher current power supply may waste energy, but won't hurt anything.

According to Ohms law, V = IR 

Where V = Voltage
I = current, in amps
R = resistance, in ohms

(voltage = current times resistance.)

Or, solving for current:

I = V/R


current = voltage divided by resistance.

So if you have a 12 volt power supply, and a 100 ohm resistor, you'll get 12/100, or 0.12 amps, flowing through the resistor.