<p>A DC-to-DC power adapter (4) includes a first DC power input portion (41), a DC-to-DC power converting circuit (43) and a first DC power output portion (42). The first DC power input portion (41) is selectively connected to an AC-to-DC power adapter (5) or a DC power connector (6) for receiving a first input DC voltage (V1) from the AC-to-DC power adapter or a second input DC voltage (V2) from the DC power connector. The DC-to-DC power converting circuit (43) is electrically connected to the first DC power input portion (41) for converting the first input DC voltage (V1) or the second input DC voltage (V2) into a first DC output voltage (V3). The first DC power output portion (42) is electrically connected to the DC-to-DC power converting circuit (43) for receiving and outputting the first DC output voltage (V3).
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