The most important figure for bypass capacitors is not really capacitance, but ESR, voltage, and ripple current rating. That being said, 22 uF is squarely in the middle of typical capacitors used for bypass applications in computers. The most critical thing is not to use capacitors whose voltage rating is too low, as they will be damaged and could explode. The highest voltage found on most of a computer is 12V, which is present on PCIe, and the VRMs for the processor. The DRAM supply will have a lower voltage, but without more information I can't tell you what that is.