OWC

OWC Mercury Helios 3

Expert rating6 / 10

External GPU EnclosuresView on owc.com

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

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Disclaimer: The price and specification of the given product may differ from the actual product. Please confirm on the retailer's website before buying.

Manufacturer: OWC Last updated: 2026-09-12

Where to buy

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OWC Mercury Helios 3 (Thunderbolt 3 eGPU Enclosure / 400W PSU / Bus-Powered Charging / Predecessor to Helios FX) 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.

Specifications

Identity

Brand	OWC

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

Model	Mercury Helios 3
GPU Compatibility	GTX 10-series through RTX 20-series, dual-slot cards
Price	Launched around $299 (2018)

Expert Review

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Solid basic Mac eGPU box, superseded by the Helios FX which OWC still actively sells.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

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)?

The OWC Mercury Helios 3 (Thunderbolt 3 eGPU Enclosure / 400W PSU / Bus-Powered Charging / Predecessor to Helios FX) is a eGPU enclosure from OWC. Key specs: Connection Standard Thunderbolt 3, PSU Wattage 400, Max GPU Length 290, Host Power Delivery 85, Extra Ports None onboard beyond the GPU's own outputs.

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

It suits 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)?

It is a poor 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.