I'm a beginner electronic hobbyist and I'm attempting to automate the lock on my door with a 12v 400 ma push pull solenoid. I've got the whole circuit pretty much up and running, using an Arduino to control a relay that cuts on and off power from a wall power supply to the push pull solenoid. Heres my problem, all the power supplies I've ordered, even if they say 12v 400ma, cause the solenoid to become extremely hot after a few minutes and I'm not exactly trying to burn down my house. Obviously in this case the power supply outputs something different then what its rated for, but I've already bought two (the first time I forgot to check the amperage rating before I bought it so that was my fault) and I don't wanna throw too much money into this. I was considering ordering a custom nicd battery instead but thats out of the question due to some battery shipping laws that require signature, and id rather go the plug in to the wall route anyway. If anyone could maybe send a link to a more competent power supply or if anyone has any other ideas, that would be extremely helpful, thank you.