Types of shore power connection found in the US
120 Volt 30 Amp Shore Power Connections

120 Volt 50 Amp Shore Power Connections

120/240 Volt 50 Amp Shore Power Connections

Looking out for problems with Shore Power Cords
Shore power cords should be regularly inspected for corrosion, melted plastic, or blackened connections. If shore power connections get salt or moisture on the conductors corrosion can cause a voltage drop across the contacts. The voltage drop produces heat which further accelerates the deterioration. Although the male prongs of the plug can be reasonably easily cleaned with a piece of sandpaper or a Dremel tool it is virtually impossible to clean the female contacts in the socket. The only way to prevent corroded contacts in the socket is to keep it sealed at all times, either with a tight fitting plug in place or with a tight fitting lid securely fastened. A small amount of WD40 sprayed into the socket might also help.
Plugs that are worn, loose, cracked, heat damaged or melted should be replaced. It is normally advisable to replace the plug and socket at the same time as heat from one will cause damage to the other. Shore power cords should be stored in a dry place and when shore power cords are not in use the male end should be plugged in to the female end to help avoid getting moisture on the connectors.
Overheated shore power plugs are a major cause of boat fires. Its not worth trying to economize on this vital area of your boats electrical system. If your plug or socket don't look right replace them before it is too late.