Will any SD card work with a Magellan GPS?

I have an Explorist 400 and it just says unlimited SD expandability…but when I took out the Magellan SD card and put in a 1 Gb regular one (not Magellan brand) it won’t detect it. Is this some sort of scam by Magellan to make sure you buy SD cards from them? Or are they somehow different cards? Or do I need to format it in the GPS to prep it for use with the system.