sun,
on regards any usb cable that fits perfect in your g1 phone and it is safe, I have never had any problem with many diferent usb cables that fits on my g1 phone, on regards chargers, you need to be very careful about that, I am not good with electricity, but the one that I have it's different than yours, I have
Input AC100-240V
output: DC 5v-1A LPS
Volts and Amperes is something completely different.
You can use the following formula:
V = W / A
V = Volt (Voltage)
W = Ohm (Resistor)
A = Ampere (Amperage)
That means you have to know the resistor to calculate the voltage.
1V carries .1A until resistance is added
Amps = Volts until you add resistance, capacitance, or inductance.
I don't know man

be very careful.