No, benchtop power supplies should not be operated on their side (horizontally), as this can block the air intake and exhaust vents. Obstructing the vents will prevent proper cooling and may lead to overheating or damage to the unit.
However, some power supplies, particularly forced-air cooled models with vents on the front and rear panels, can be operated horizontally. Please refer to your product's user manual to confirm the proper installation and orientation.
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