Arcade machines, like all electronic equipment, require proper protection against reverse polarity to prevent damage from incorrect power supply connections. The most common protection methods include:

1. Diode Protection: A simple diode is placed in series with the power input. This allows current to flow only in the correct direction, blocking reverse current. While effective, it causes a voltage drop (typically 0.7V for silicon diodes) which might not be suitable for all applications.

2. MOSFET Protection: Using a P-channel or N-channel MOSFET provides low-voltage drop protection. The MOSFET acts as a switch that only conducts when proper polarity is applied. This method is more efficient than diode protection but slightly more complex.

3. Fuse with Diode: A fast-blow fuse combined with a reverse-biased diode across the power input. During reverse polarity, the diode conducts and blows the fuse quickly, protecting the circuitry.

4. Bridge Rectifier: A full-wave bridge rectifier automatically corrects polarity issues, ensuring proper operation regardless of input polarity. This method is reliable but introduces higher voltage drops.

Most commercial arcade machines typically use diode or MOSFET protection due to their balance of cost, reliability, and efficiency. Proper polarity protection is crucial for preventing damage to PCBs, power supplies, and other sensitive components in these vintage gaming systems.