We consider the problem of Simultaneous Wireless Information and Power Transfer (SWIPT) over a fading multiple access channel with additive Gaussian noise. The transmitters, which are energy harvesting, have a delay sensitive and delay tolerant data to send. In addition to harvesting from an ambient perennial source, the receiver can harvest from the incoming radio frequency (RF) data stream, if required. Assuming an ideal co-located receiver architecture, we characterize the minimum-rate capacity region which provides the fundamental limit of transmitting multiple classes of data and power simultaneously. Next, we derive the minimum-rate capacity regions for two popular practical receiver architectures namely, the time-switching and power-splitting receiver. We show that power-splitting receiver although more complex, provides a larger capacity region.