I would say that Fiber supplements are generally unnecessary as there are plenty of foods that will give you all that you need. As for 25 grams that is the generally accepted RDA, but most people need more. You don't want to go nuts with it as too much fiber is unhealthy, but 40-50 grams is okay.
Most days I'm between 35-50 grams. what I typically use is:
Oatmeal — two servings, I use Bob's Red Mill steelcut oats or 10-grain hot cereal.
Multi-grain wraps — some are 10-12 grams per wrap for 100 calories
Lentils — add a little spice to them and they're great, and 10-12 grams
Usually, add one of these things to the diet each day and this is about a third of my target to get over 35 grams.
After that, whole grain cereals, veggies and fruits.
As budget is a concern for most of us, the wraps are a little pricey; oatmeal and lentils are dirt cheap. Good luck with it.