Below is a list of voltage levels that are specified in certain documents as official, as well as examples of consoles or systems that output different voltage level standards.
I will define two voltage levels, terminated (connected to receiver like TV) and floating. This will presume the system is using a 75R resistor in order to form a 50/50 voltage divider when connected to a receiver, but if the system is different and using another termination resistor value, you would have to calculate the expected output voltage from that new voltage divider or just connect it to a receiver to measure the voltages.
Composite has all of its signal on a single pin, and its voltage range is 1V terminated / 2V floating.
This comprises of the Sync pulse expected to be 0.3V terminated / 0.6V floating, and the luma/chroma expected to be 0.7V terminated / 1.4V floating.
RGBs is RGB and CSync signals.
Just like composite, the voltage levels of RGB and sync signals match the composite video standard.
Red, Green and Blue lines should be 0.7V terminated / 1.4V floating from 0 to 100% saturation.
The CSync voltage should be 0.3V terminated / 0.6V floating.
There is a variant of the CSync signal called TTL, where the voltage should be 2.5V terminated / 5V floating. This is used in systems like arcade machines typically.
The RGB voltages are also usually then 2.5V terminated / 5V floating for the RGB also.