Define the supply disturbance to control
A local capacitor can supply transient current and provide a path for unwanted supply variation, but its usefulness depends on the connected circuit and layout. Start with the device requirements, supply network and expected load behavior.
Bulk energy storage and local high-frequency bypassing address different parts of the problem. The terms decoupling and bypassing often overlap in practice. A label on a schematic does not specify the required impedance or prove that a capacitor is effective at the relevant frequencies.
Select the actual component
Consider capacitance, tolerance, voltage rating, dielectric behavior, ESR, ESL and package. Effective capacitance can depend on applied bias and temperature. Use the manufacturer data for the exact part rather than assuming the printed nominal value is available under every condition.
For regulators and other feedback-controlled supplies, observe the specified output-capacitor and stability requirements. Adding an arbitrary mix of values is not always beneficial. Review resonances and the interaction of the network when the performance requirement justifies it.
Place for a short, deliberate current loop
Inspect the connection from the device supply pin through the capacitor and back to the relevant return. Trace and via geometry contribute impedance. Physical closeness alone can be misleading if the route creates a long or indirect loop.
Coordinate local placement with the plane arrangement, pin escape and assembly clearances. Check both populated sides and the actual via connections. Preserve the important geometry when rerouting nearby signals or changing the component package.
Measure the relevant behavior
Define acceptable supply variation and operating conditions. Use a probing method that does not add a large unintended loop or obscure the frequency range under investigation. Compare the result at the relevant device connection, not only at the power-entry connector.
Record the BOM, layout and load configuration with the result. A part substitution can change the effective network even when its nominal capacitance matches. Keep approved alternatives and any required validation tied to the product revision.