I'm using a small 130 litre box freezer that's on a timer switch to control the temp. I have 2 fishtank pumps pumping fresh air into the freezer through 2 pipes t& thus the top is open a lil but for air to escape. I want to add a small cpu fan to circulate the air, but need a 2nd hand power supply to do so as it blows up if it gets plugged in directly. lol