On my i3 clone I've been trying to add the Anycubic i3 Ultrabase to my RAMPS 1.4 board and after adding the necessary configurations in the Marlin firmware I can heat up the bed. The issue is that it is very slow - it gains about 1 °C every 20-30 seconds - and the indicator LED and LED 2 on my RAMPS board blinks randomly whilst it is heating. Furthermore when the LCD is powered from the printer it starts flickering too. I'm guessing this is a power issue, especially since when I plug it directly into a power source (instead of a splitter) the LED blinks less often and if I unplug the bed but 'turn it on' the LED is solid, but I'm not sure what can be done.
Upon further inspection - the voltage input to the board is a constant 12 V however the output from D8 is ranging from 5 V to 12 V and fluctuating rapidly.