I had my 3D printer powered by dual 24 V PSUs wired in parallel and my heatbed was wired into the main using a SSR to help power it. I replaced the two PSUs with a single Corsair 750 W ATX. My printer runs smoother and there's much less wiring clutter to deal with but now no matter what the heatbed will not heat up.
The main connection of the ATX I purchased is an 8 pin connection so I tried using all 4 wires to power my printer and it didn't make a difference, I tried using the SSR again using 2 connections from the ATX leaving the other 2 to run the motherboard but that didn't work either. I even tried MOSFET and that also failed. I don't see why the Heatbed no longer heats up yet the thermistor is more accurate and working properly since my switch to the ATX, do I need to go up to a 1000 W ATX instead? I can't imagine what more I could do.