Seasonic Platinum 1200W Modular Power Supply Review

Seasonic are using a San Ace 120 (model 9s1212h403) fan. This is a Sanyo Denki unit which uses three balancing points instead of two. This helps to achieve perfect balance and rotation.

The 1200W power supply has a new ‘Hysteresis' feature. This optimises how frequently the fan switches off and on. At 25c ambient temperature the fan turns on when the load rises above 35% and it turns off when the load drops below 25%. Due to this lag in response the fan switches on and off less frequently which reduces power loss in Fanless and Silent Mode.

This is a Seasonic XP3 design which we have seen in a slightly different guise in our recent review of the Cooler Master V1200 Platinum power supply. The soldering quality is excellent throughout.


Behind the AC receptable is a sealed PCB which is home to some of the components of the EMI filter – a single X cap, four Y caps and a CM choke. The other components of the filtering stage are on the main PCB, which include an MOV, two pairs of Y and X Caps and two more CM chokes.

The primary side is a full bridge design with an LLC converter for lossless switching. The secondary side uses a synchronous design with +12V fets on the main PCB. The DC-DC converters are installed on the modular PCB to help reduce power loss.

The main PCB and modular PCB incorporate high grade Japanese electrolytic and solid capacitors.

Seasonic are using three high grade Japanese capacitors on the primary stage (class leading ‘Nippon Chemi Con'). These are 105c rated. All three are rated 390uF 420V. This is different to the Seasonic XP3 powered Cooler Master V1200 Platinum which we reviewed several weeks ago. The Cooler Master unit uses lower specification capacitors – one rated 390uF 420V and the other two 330uF 420V.

Become a Patron!