It is possible to change the video format on the SPE-420 & SPE-1640 encoders from PAL to NTSC and vice versa
On the webpage of the SPE, go to Setup -> Video & Audio -> Video Setup and then in the CVBS Type file you can choose either NTSC or PAL
Unfortunately this option is not available on the SPE-1610:
The SPE-1610 & SPE-1610A will have the video format defined by the device itself. You can determine the video format from the model number listed on the device, P will denote a PAL device and N will denote a NTSC device: