you will need not only a 24V power supply but also a 24V heater for the bed, 24V hot end and 24V fans.
Current will be half of the current you consume at 12V. Power should remain the same.
Some people use a separate power supply for the bed. In that case one has to install a wire between both - (minus or negative) connections of the power supplies.
A SSR (DC) is always preferred over the MOSFET on the controller.
For a 280W bed current will drop from 23,3A to 11,7A. See my post in heated beds for wire gauge. The thicker the better.
I'm making a separate safety processor using an Arduino. This would make it easier for most 3D-ers to implement this as they know how to flash Arduinos.
design parameters :
- overtemperature bed
- overtemperature heatsink @ hot end
- if one of these input parameters is triggered, power to heaters will be cut using a normal (mechanical) relay.
- indication status using LED's (green OK-led , red BED error, red hot end error, red smoke error)
- reset button
- separate power supply
- trigger levels can be set in firmware as one is used to for i.e. Marlin.