12v radio power supply from different PSUs?

Question

Electronics

The scheme is as follows:
consumer - car radio (12v) power supply 220v.
12v power supply from a 300 watt power supply unit (turns on the "unit" by supplying a phase to additional devices, in our case, a 220v power supply unit for 12v - 300 watts). But when the "unit" is turned off - this PSU is turned off and the settings, etc., disappear accordingly. It is necessary to organize a constant power supply and through the manager (there is such a + on the radio) to give +12 when the unit starts up. So 2 bp. One independently feeds, the other turns on and off.
The question is - according to the idea of ​​\u200b\u200b2 different PSUs - you need to combine the earth -? Please clarify if I don't understand something.
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*PSU - Power Supply.

Answer 1

Usually you can, now almost all power supplies are galvanically isolated from the network. The second power supply that connects to the red wire of the radio (memory) can be very low power. There 100-200 milliamps maximum, in standby mode. Although, when connected to a car, for example, you need to include a yellow wire in the ignition circuit, or in winter, for a couple of days, the battery of average scall lands in such a way that it will not start later. Earth (minus power) must be connected so that the voltages are considered from the same potential level.

Answer 2

It is convenient to use a computer power supply for the car radio, the computer power supply has a special + 5vsb output, there is 5 volts even when the power supply is turned off (the main thing is that it is plugged into the outlet).
You can put a boost converter on the 5vsb output and raise it to 12 volts, these 12 volts are on the yellow wire of the radio.