# Why the replacement of 7812 with R-78E12-0.5, DC/DC makes the circuit not working?

I have this simple surge protector and soft start inside the PSU. My transformer is out of its specifications yields 21.3V after bridge rectification. And 0.1A load (12V fan for cooling pass transistor) makes the 7812 very hot (despite it has a heatsink). So i decided to replace the 7812 with R-78E12-0.5 as it is a pin-2-pin replacement to 78xx. But after i did it, the CD4027 started to do weird things... after I push the On/Off tactile switch the National Semiconductor 4027 always switch the relays ON and TI CD4027 always OFF. I have desoldered the R-78E12-0.5 out and put the 7812 back - and the circuit is working as it should be...

UPDATE: After the answers of user287001 and Huisman I have completely reworked the Soft Start. The simulation worked. Will try it on breadboard in couple of days.

The CD4027 draws uA, so it hardly contributes. And further loads are the 100k$$\ \Omega\$$ plus 2.2k$$\ \Omega\$$ .
Do place a 1.2 k$$\ \Omega\$$ between the output and the ground of the R-78E-12-0.5 and check whether that helps.