Basically - If your camera takes SD cards it may not take SDHC or SDXC. ...they will physically fit, but it's about unseen 'standards.' --somewhere, someone thought
"having one standard is good, so having even more standards must be better."
Anyway, the newer standards may or may not play well w/ your older devices.
edit, ...but newer devices can take the older SD standards (backwrd compatible)