Different schools:
- 10 ohm and capacitor near power header (this basically results in an RC low pass filter, but with a voltage drop over the resistor depending on the current). Usually somewhat pointless (the resistors, not necessarily the capacitors).
- 10 ohm without capacitors (either using them as fuses, expecting them to die if something’s shorted, or possibly just cargo culting, trying to do the above but forgetting how things work, see “power sins” here for more).
- Ferrite beads (if done right, this can form an LC filter, but is usually cargo culting, see here).
- Series diodes (using Schottky diodes with a low voltage drop, e,g, 1N58xx). Not a bad idea, if you don’t trust yourself (or are building production stuff for others who don’t trust themselves).
- A slighly fancier polarity protection is to use MOSFET transistors; they’re available with extremely low drain-source resistance (tens of milliohms) so the drop will barely be noticeable even with higher power requirements.
- EDIT: Even fancier is to use a dedicated supply controller (example) with the MOSFETs; they can protect against a whole lot of issues. Probably overkill for synth modules.
- Polyfuses (see discussion here).
- EDIT: Diodes between the rails and ground. This will short the supply if you hook it up backwards, under the assumption that the power supply is better prepared to deal with a short than the module is to deal with supply reversal (see the polyfuse link for an example).
- EDIT: Rectifiers on the way in – using a few more diodes, you can simply route the voltages to the right rail, no matter how they’re connected. This allows the user to plug in the power either way. Drawback is more components and a higher voltage drop.
Bypass capacitors should be close to the power pins for the respective chips. Note that the bypass caps in your schematics are too tiny for most circuits; 0.1 uF (100 nF) is the usual size, some argue that with modern components 1 uF multilayer ceramics would make even more sense.