Will I need an additional power supply to use the DSC PTK5507?
Not necessarily, but the keypad does use a fair amount of current so it is very possible that you will. Let's go a little deeper and look at how you can determine whether you need any more power.
The first thing that you need to know is that the DSC PC1616, PC1832, and PC1864 have a maximum power output of 700 mA on the auxiliary power and keybus combined. We always recommend leaving a 10% buffer as well to be on the safe side which leaves you with 630 mA. Now you will want to figure the current draw based on the maximum current so that the system does not overdraw and shut down at an inopportune time. The DSC PTK5507 uses 200 mA per keypad. But it also has a high power mode if you need a brighter screen that increases that to 300 mA. Just make sure that you use the number for the correct mode in your calculations.
Then you will have to take into consideration all of the other power drawing devices attached into your system on the auxiliary or keybus terminals. This includes any other keypads, communicators, zone expansion boards, motion detectors, smoke detectors, glass break detectors, et cetera. You can find the current draw for these devices easily by looking in the installation manual for each one under the specifications.
Once you add all those numbers up, if you are at about 630 mA or less then you will not need any additional power supply modules. But if it is higher than that, you will need power supply modules to keep the system from shutting down due to excessive current draw.
The recommended device to use with the DSC PowerSeries is the DSC PC5204. The DSC PC5204 is a bare circuit board so you will need the PC5003C cabinet to put it in, or a similar housing. Unfortunately the PC5204 will not fit in a cabinet with the main board. The PC5204 is too wide to fit on the side of the cabinet and you will need a backup battery for it as well as the main board in the cabinet. So there would not be room below the main board either. The PC5204 provides up to 1 amp of current so it will most likely cover everything you need in addition to the main board's current limit. But you can add more than one if needed.