I think you need something simple and cheap, a suitable delay circuit is not a problem to build at home, unless you care about exact timing (up and down for a few seconds) build the connection that I uploaded to the Internet at the address http://www.tetrofet.sk/casovac.gif . RC article 220k is in charge of the entire timing, 100uF, by changing the values of these two components, you set the delay time. Diode D1 protects the IO CD input 4093 and, together with the resistor connected to the supply voltage, contributes to the rapid discharge of C1 after the power is turned off, so even after a short power cut, the relay will turn on again with a delay. Gate H2 after increasing the voltage on C1 to approximately 1/2 supply voltage will change the state at the log output. 1 that log. 0, gates h1, H3 and H4 invert this signal, so a log appears on their output, 1 and transistor BC547 opens (548 ap.) which turns on the relay. If you want to use a 12V relay, without changes, you can also power this timer with 12V voltage (even directly from one of the two adapters that you need to switch on immediately, but only if it is stabilized, otherwise it could cause problems). Stabilizer of course 7805 and you will then omit the 10uF capacitor and it will probably be necessary to adjust the values of the RC cell. With the indicated values, I had a delay of approx 55 seconds. I also have to point out that the set time can vary, because the tolerance of the electrolyte capacity is quite large and the set time also depends on the leakage current of the electrolyte C1
73!
Roman Žipaj – OM0ARZ