How many volts are in 600 watts?

You are confusing electrical potential (Volts) and power (Watts).

The equation for power (watts) is P = VI where V is volts (a measure of electrical "pressure") and I is current in amperes (the rate of flow of electricity).

If the system is 120V and the power used is 600W then the current used is 5A.

If the system is 240V and the power used is 600W then the current used is 2.5A.