Philtre capacitors. The term used for the large capacitors used to philtre out the residual AC ripple in the power supply. The rectifier converts AC to pulsating DC, since it just allows current to flow in one direction. The output of the rectifier is a series of "humps", which must be "smoothed out" to become flat, ripple-free direct current. The philtre caps store up the voltage on the positive rise of the pulsating rectified AC waveform, and hold it there while the rectified waveform goes down to zero. This charge, hold, charge, hold, etc. behaviour is what smoothes out the ripple. In general, the larger the capacitor, the less residual ripple there will be.