They do use a lot of samples (mostly bass stabs), but otherwise it can be a chain of distortion plugins applied to a simple synth sound. For example, try adding a WOW filter, iZotope Trash2 and FF Saturn in sequence to a simple Sylenth1 patch and see what happens. You need to be careful with the plugin parameters to find the sweet spot (otherwise it just sounds like a distorted mess). Layering also helps (i.e. use a separate sub layer underneath).