In most cases, yes. ATX is what is used in most models now, some are just form factor models, while others are your usual 'regular' model. Check to make sure you have the right Wattage requirements for what you want do on your computer.
ATX is a form factor, not a performance rating. Most computers on the market today use the ATX format. Other formats you may have noticed, such as BTX and ITX, are specialized power supplies that are made specifically for miniature PC's.
ATX is a formfactor, not a brand. To find a good power supply check some articles on tomshardware.com that compare effiency and noise and such criteria over various models.