  We consider the problem of Simultaneous Wireless Information and Power
Transfer (SWIPT) over a fading multiple access channel with additive Gaussian
noise. The transmitters as well as the receiver harvest energy from ambient
sources. We assume that the transmitters have two classes of data to send, viz.
delay sensitive and delay tolerant data. Each transmitter sends the delay
sensitive data at a certain minimum rate irrespective of the channel conditions
(fading states). In addition, if the channel conditions are good, the delay
tolerant data is sent. {Along with data, the transmitters also transfer power
to aid the receiver in meeting its energy requirements.} In this setting, we
characterize the \textit{minimum-rate capacity region} which provides the
fundamental limit of transferring information and power simultaneously with
minimum rate guarantees. Owing to the limitations of current technology, these
limits might not be achievable in practice. Among the practical receiver
structures proposed for SWIPT in literature, two popular architectures are the
\textit{time switching} and \textit{power splitting} receivers. For each of
these architectures, we derive the minimum-rate capacity regions. We show that
power splitting receivers although more complex, provide a larger capacity
region.
