OWC

OWC Mercury Helios 3

Expert rating6 / 10

Connection:: Thunderbolt 3
PSU:: 400W
GPU Fit:: Full-length, dual-slot
Type:: Bare enclosure

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Manufacturer: OWC Last updated: 2026-09-12

OWC Mercury Helios 3 Review

If you're comparing OWC's original Mercury Helios 3 against the newer Mercury Helios FX to figure out which Thunderbolt 3 eGPU box to buy,

the short answer is the Helios FX replaced it and is the one OWC still sells, so only go for a used Helios 3 if the price gap makes it worth 15W less laptop charging and a smaller 400W PSU.

What It Actually Is

The Mercury Helios 3 was OWC's first Thunderbolt 3 eGPU chassis, a bare aluminum enclosure with a 400W internal supply, 85W of USB-C charging, and room for a dual-slot card up to 290mm. Like most Mac-focused boxes, it skips USB hubs and Ethernet, since Thunderbolt 3 Macs already have those ports.

Comparison to Alternatives

OWC's current Mercury Helios FX is the direct successor and the one to buy new, it keeps the same bus-powered, Mac-focused philosophy with a slightly larger 500W supply. Against the AKiTiO Node Titan, the Helios 3 has similar charging power but the Node Titan's 650W PSU has more headroom for bigger cards, so budget-focused Mac users should weigh a used Helios 3 against a new Helios FX rather than buying this one at full price.

Our verdict

Reviewed by Burooj Alam. Rated by us, not by users.

Expert rating6 / 10

Solid basic Mac eGPU box, superseded by the Helios FX which OWC still actively sells.

Best for

Mac users who find a used unit cheap and just need a bare Thunderbolt 3 enclosure
Buyers who don't need USB hub or Ethernet ports on the enclosure itself
Simple, no-frills dual-slot GPU builds under 400W

Not for

Anyone buying new, since the Mercury Helios FX replaced it with more PSU headroom
Cards that need more than 290mm of clearance
Windows users wanting extra I/O built into the box

Specifications

What these specs mean

Identity

Brand	OWC
Model Number	Mercury Helios 3

Connectivity

Connection Standard	Thunderbolt 3
Extra Ports	None onboard beyond the GPU's own outputs

Power & Compatibility

PSU Wattage	400 W
Host Power Delivery	85 W
Max GPU Length	290 mm
Cooling Type	Active Fan

FAQs

What are the key specifications of the OWC Mercury Helios 3 (Thunderbolt 3 eGPU Enclosure / 400W PSU / Bus-Powered Charging / Predecessor to Helios FX)?

Key specs for the OWC Mercury Helios 3: Connection Standard Thunderbolt 3, Extra Ports None onboard beyond the GPU's own outputs, Cooling Type Active Fan, GPU Compatibility GTX 10-series through RTX 20-series, dual-slot cards.

Who is the OWC Mercury Helios 3 (Thunderbolt 3 eGPU Enclosure / 400W PSU / Bus-Powered Charging / Predecessor to Helios FX) best suited to?

Best suited to: Mac users who find a used unit cheap and just need a bare Thunderbolt 3 enclosure; Buyers who don't need USB hub or Ethernet ports on the enclosure itself; Simple, no-frills dual-slot GPU builds under 400W.

What are the drawbacks of the OWC Mercury Helios 3 (Thunderbolt 3 eGPU Enclosure / 400W PSU / Bus-Powered Charging / Predecessor to Helios FX)?

Not the best fit for: Anyone buying new, since the Mercury Helios FX replaced it with more PSU headroom; Cards that need more than 290mm of clearance; Windows users wanting extra I/O built into the box.