1) imo, the 12v load put on 5v means is no longer 25w, but you could measure the resistance of the light bulb directly and math out how much it would draw at 5v.
2) I dont see different rails on the picture label. If it would of had different rails it would of said something like 12v1 and 12v2, each on its row in the table and consumption limits for each. So i guess this one doesnt have different rails, and also instead of just using one single connector, you could practically tie more 12v wires together to avoid having all the 18 amps through just 1 single wire.
3) perhaps 18a may simply not be enough, but also perhaps you may have a short on the hotend or bed and then changing the psu wont make a difference; i would check and measure resistances of heated bed and see exactly how much current it draws, also check hotend resistance (for shorts etc), then sum up all the consumers, which should be something like 12A for bed, probably 1,76A for hotend, and roughly around 1A for each driver, so this puts the psu quite near its limit.
The heated bed is by large the biggest consumer. So first thing i would do is disconnect the bed and check if everything else works ok as long as that is off.
2) I dont see different rails on the picture label. If it would of had different rails it would of said something like 12v1 and 12v2, each on its row in the table and consumption limits for each. So i guess this one doesnt have different rails, and also instead of just using one single connector, you could practically tie more 12v wires together to avoid having all the 18 amps through just 1 single wire.
3) perhaps 18a may simply not be enough, but also perhaps you may have a short on the hotend or bed and then changing the psu wont make a difference; i would check and measure resistances of heated bed and see exactly how much current it draws, also check hotend resistance (for shorts etc), then sum up all the consumers, which should be something like 12A for bed, probably 1,76A for hotend, and roughly around 1A for each driver, so this puts the psu quite near its limit.
The heated bed is by large the biggest consumer. So first thing i would do is disconnect the bed and check if everything else works ok as long as that is off.