I already have a basic filtration housing under the sink, but I am not sure if I am stuck buying the same brand of cartridge forever. The current filter is a standard looking size, and I like to switch to a carbon block cartridge for better taste and smell. Has anyone used carbon block filters in universal housings without changing the whole setup?

Yes, they can fit if the housing is actually a universal size, but you really have to check the dimensions before ordering. A lot of undersink systems use 2.5x10 cartridges, while bigger setups may use 4.5x10 or even 20 inch filters. I had a similar setup at home and only replaced the cartridge, not the entire housing. While comparing under the sink water purification systems, I noticed they carry carbon block filters for their own unit and for common universal housings too. I look at the cartridge length, diameter, gasket style, micron rating, and NSF/ANSI 42 certification before switching.

Keeping the old cartridge label or taking a photo of it before replacing anything is a small thing that helps a lot. It makes it easier to compare size, flow direction, and replacement details later, especially when ordering online where product descriptions are not always written clearly.