Here’s a tutorial from Maxim describing the differences between switch mode, linear, and pulse Li Ion battery chargers. Advantages and disadvantages of each are covered by the article.
There are three methods to charging Li+ batteries: switch-mode, linear and pulse. Each method has its advantages and disadvantages. Switch-mode charging minimizes power dissipation over a wide range of AC adapter voltages, but consume more board space and add complexity compared to linear and pulse charging. Linear chargers are small and great for noise sensitive equipment, but power dissipation is high. Pulse chargers are small and efficient, but require a current-limited AC adapter. Select the charging method based on the prioritization of cost, space and efficiency.