Personal Shield Generator (PSG) is a type of armor that is worn as a belt. PSG's are small electric fields that can absorb some damage from Energy damage ranged weapons. As the generator absorbs damage, its charge is reduced, reducing its effectiveness. Once you are no longer under attack, the generator will slowly charge back up. Personal Shield Generators can be crafted by Armorsmiths. Many variations of the PSG exist including Mark I-III, Imperial Prototypes, Droideka PSGs, and Old Republic PSGs.
The highest possible additional protection is 2499, when the generator is fully charged. When combined with top armor protection, a shield generator can be quite effective. However, they only protect against ranged energy damage, so will not do anything versus a lightsaber.
Note: Only the Droideka PSG can be crafted without encountering the conductivity bug. This will give the Droideka PSG higher resists and a better recharge rate then all of the other PSGs.