Not sure if power supply issue or something else

Okay so I just bought a Tronxy X5s and upgraded it, and while it gives some very nice prints, the problem is this:

Since the power supply that came with it is too weak to run the whole thing, I bought another 24V supply and mosfet to have that solely run the heatbed, everything else is still on the 360W 12V power supply also upgraded the board to a Geeetech GT2560, The problem right now is this, during print, more often near the beginning of the print, and (though very rare after the first one) at random points during the print, the temp would as mentioned suddenly drop from 200C to 190C (basically 5-10C lower than what's wanted) in about 10 secs, Sometimes it would heat up fast enough to no have the thermal runaway please reset issue happen, but sometimes not and then the thermal runaway happens, is it a power supply issue? I'm currently using a PC with Repetier to control and print from the PC, which is getting the files from a micro sd card since I don't have an octopi set up just yet for it.