I'ts generally a bad idea to try to connect two power supplies (or two separate outputs from one supply) in series, especially if they are rated for different output currents.

---

Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Quote
villainous
The power supply I have has two outputs, so if I were to tie them together theoretically I could get 24V into the printer.

In addition to dentist's point, it is also quite likely that the 2 outputs of your power supply are not galvanically isolated from each other, so that they share a common ground. In this case trying to combine them in series would result in a short.

Most RAMPS boards have capacitors rated at 16V, so you can't use 24V supplies with them except on the bed heater circuit. Can you change the resistor?

---

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].